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OUTLINES 


OF 


HUMAN    PHYSIOLOGY 


F.  SCHEXCK,  M.D.,  and  A.  GURBER,  M.D.,  Ph.D. 

Assistants  in  the  Physiological  Institute  at  Wilrzburg 


AUTHORIZED  TRANSLATION  FROM  THE  SECOND 
GERMAN  EDITION 


WM.    D.    ZOETHOUT,    Ph.D. 

WITH  A    PREFACE 
BY 

JACQUES   LOEB,    Ph.D. 

Professor  of  Physiology,  University  of  Chicago 


NEW    YORK 

HENRY   HOLT   AND   COMPANY 
1900 


Copyright,  1900, 

BY 

HENRY   HOLT  &  CO. 


"YY'Wt'cJL 


ROBERT   DRUMMOND,    PRINTER,    NEW   YORK. 


PREFACE  TO  THE  AMERICAN   EDITION 

As  the.  publishers  wish  me  to  write  a  preface  to  the 
translation  of  Schenck  and  Giirber's  "Outlines  of  Human 
Physiology, ' '  I  will  briefly  state  my  reason  for  having 
recommended  the  translation  of  this  book.  It  seems  to  me 
that  the  present  text-books  of  human  physiology  no  longer 
adequately  express  our  knowledge  of  the  laws  of  life 
phenomena.  A  number  of  facts  which  throw  new  light  upon 
the  subject  have  been  established  by  the  extension  of  physio- 
logical research  to  Invertebrates,  by  the  recently  developed 
experimental  or  rather  physiological  morphology,  and  by 
the  application  of  physical  chemistry  to  physiological  prob- 
lems. It  is  uncertain  how  soon  these  new  results  will  be 
embodied  in  the  text-books  of  human  physiology.  The 
student  will  have  to  acquire  his  knowledge  of  these  new 
subjects  for  the  present  from  the  study  of  monographs.  In 
order  to  give  him  the  time  to  do  this  the  contents  of  the 
traditional  text-book  of  human  physiology  should  be  made 
accessible  to  him  in  a  more  condensed  form.  To  my  knowl- 
edge no  book  answers  this  purpose  better  than  Schenck  and 
Giirber's  manual. 

I  have  had  no  connection  with  the  translation.  The  credit 
as  well  as  the  responsibility  belongs  entirely  to  Mr.  Zoethout. 

Jacques  Loeb. 

University  of  Chicago,  November  2,   1900. 


Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 

Open  Knowledge  Commons  (for  the  Medical  Heritage  Library  project) 


http://www.archive.org/details/outlinesofhumanpOOsche 


AUTHORS'   PREFACE 

AMONG  the  students  of  medicine  there  exists  a  need  for  an 
outline  of  human  physiology  which  contains  its  most  impor- 
tant facts  in  a  concise  form  and  gives  the  beginner  a  clear 
view  of  the  entire  field.  It  is  true,  such  manuals  exist — 
those  of  Oestreich,  Breitenstein,  Schmidt,  Peter,  etc. — but 
as  these  contain  many  errors,  they  can  hardly  be  regarded 
as  aids  to  the  student,  although  in  general  use.  For  this 
reason  it  appeared  advisable  to  publish  this  manual. 

In  regard  to  the  arrangement  of  the  material,  we  believe 
that  we  have  not  deviated  to  any  great  extent  from  the  old 
and  tried  system.  Our  object  has  been  to  lay  stress  upon 
the  undisputed  facts,  while  we  have  not  entered  into  the  dis- 
cussion of  various  unsettled  questions.  Yet  in  some  in- 
stances we  were  compelled  to  mention  the  various  hypotheses 
at  present  advanced. 

The  physiological  methods  are  dealt  with  very  briefly  and 
often  merely  indicated  by  a  few  words,  as  it  was  not  our  in- 
tention to  give  elaborate  descriptions  of  methods  and 
apparatus.  Moreover,  by  a  shorter  presentation  of  the 
methods  the  erroneous  notion  might  be  called  forth  that  but 
little  is  necessary  to  understand  it.  Hence  a  mere  allusion 
seems  preferable,  so  that  the  student  shall  realize  that  this 
manual  does  not  contain  all  that  he  needs  to  know,  but  that 
it  gives  only  a  survey  of  the  general  field  of  physiology  and 
cannot  take  the  place  of  lectures  and  larger  text-books. 

Most  of  the  illustrations  of  this  book  are  copies  of  figures 
found  in  well-known  text-books  and  original  papers.  Many 
of  the  figures  have  been  kindly  loaned  by  the  publishers  of 


VI  AUTHORS'    PREFACE 

Bernstein's  Lehrbuch  der  Physiologie  (Figs,   i,  14,   16,   17, 

32-34,  37,  39-44,  46-48,  and  51-53).  We  are  indebted 
to  F.  C.  W.  Vogel  (Leipzig)  for  the  plates  of  Figs.  5-8 
(from  Hermann's  Handbuch  cler  Physiologie,  Bd.  V),  to 
Edward  Besolt  (Leipzig)  for  the  plates  of  Figs.  19,  22,  24, 
45,  49,  and  50  (from  Rauber's  Anatomie,  etc.),  and  to 
Fischer  (H.  Kornfeld,  Berlin)  for  Fig.  23  (from  Lenhossek : 
Der  feinere  Bau  des  Nervensystems). 

We  are   especially  indebted  to   Professor  I7ick  for  advice 
received  in  the  planning  of  this  work. 

Dr.   F.  SCHENCK. 

Dr.  A.  GURBER. 
Wurzburg,  October,  1897. 


TABLE  OF  CONTENTS 


PAGE 

Authors'  Preface v 

Introduction.     General  Physiology i 


SECTION  I 
metabolism 

CHAPTER 

I.  The  Chemical  Composition  of  the  Human  Body 12 

II.  The  Blood 52 

III.  The  Gases  of  the  Blood  and  the  Chemistry  of  Respiration  58 

IV.  The  Circulation  of  the  Blood 63 

V.  Respiratory  Movements 80 

VI.   Lymph,  Lymph  Glands,  and  Spleen 87 

VII.   Secretions 91 

VIII.  Nutrition , 114 

IX.  The  Digestion  of  the  Foodstuffs 123 

X.   Absorption  and  Assimilation  of  the  Foodstuffs 141 

XI.   The  Changes  of  Blood  in  the  Organs  and  Internal  Secre- 
tions    149 

XII.   Metabolism 155 

SECTION  II 

THE  TRANSFORMATION  AND  SETTING  FREE  OF  ENERGY 

XIII.  Animal   Heat 178 

XIV.  General  Muscle  Physiology 1 84 

XV.  Special  Physiology  of  the  Muscles 201 

XVI.  General  Nerve  Physiology 215 

XVII.   The  Spinal  Cord 226 

XVIII.  The  Brain 235 

XIX.   The  Peripheral  Nerves  and  the  Sympathetic  System.  .  .  .  250 

XX.   Sense  Organs  in  General 255 

vii 


vni  CONTENTS 

CHAPTER  PACE 

XXI.   Optics 257 

XXII.     The  Ear 285 

XXIII.  Smell 296 

XXIV.  Taste 298 

XXV.  Cutaneous  Sensations 300 

XXVI.   (  >rgan  Sensations 305 


SECTION    III 
REPRODUCTION  AND  DEVELOPMENT 

XXVII.    Reproduction 307 

XXVIII.    Physiology  of  the  Embryo 313 

XXIX.    Pregnancy,  Parturition,  and  Childbed 324 

XXX.   Development  of  the  Body  after  Birth 327 

Index 333 


HUMAN    PHYSIOLOGY 


INTRODUCTION 

PHYSIOLOGY  is  the  science  of  normal  life.  It  may  be 
divided  into: 

i.  General  Physiology,  i.e.  the  science  of  the  general 
properties  of  life  or  of  the  character  of  the  living  substance. 

2.  Special  Physiology,  i.e.  the  science  of  the  vital 
phenomena  of  individual  living  beings  (e.g.  man,  animals, 
plants),  and  of  the  single  organs  of  the  living  beings. 

This  manual  treats  of  the  essentials  of  human  physiology. 
As  an  introduction,  a  brief  survey  of  general  physiology  is 
prefixed. 


GENERAL  PHYSIOLOGY 

1.   METABOLISM.      IRRITABILITY 

The  living  body  contains  no  other  elements  and  forces 
than  those  found  in  the  inanimate  world.  There  is  no 
special  "  Vital  Force.  "  The  properties  of  life  are  dependent 
upon  the  chemical  and  physical  properties  of  the  living  sub- 
stance. The  composition  of  this  substance  is  not  known; 
in  fact,  it  is  a  question  whether  it  is  chemically  an  indi- 
vidual substance  or  a  mixture  of  different  bodies. 

The  vital  processes  comprise  chemical  and  physical 
processes — the  changes  of  matter  and  energy  [metabolism]. 

Metabolism  consists  of  two  processes:  On  the  one  hand, 
the  living  being  continually  splits  up  and,  by  the  addition  of 

i 


2  HUMAN  PHYSIOLOGY 

oxygen,  oxidizes  the  organic  compounds  which  compose  its 
bod\-.  thereby  forming  simple  compounds  (carbonic  acid, 
water,  ammonia  and  simple  ammonia  derivatives,  e.g.  urea); 
on  the  other  hand,  it  again  builds  up  its  body  substance 
from  materials  of  the  outer  world.  The  former  process  is 
called  dissimilation  ;  the  latter,  assimilation. 

The  power  of  assimilation  varies  in  different  living  beings. 
Plants  containing  chlorophyll  are  able,  in  the  presence  of 
sunlight,  to  assimilate  very  simple  compounds  (e.g.  carbonic 
acid,  water,  nitrates),  oxygen  being  set  free.  Certain  Bac- 
teria can  assimilate  free  nitrogen.  Animals,  however,  do 
not  form  their  body  substance  from  inorganic  but  from 
organic  compounds  which  they  obtain  as  foods  from  the 
plants.  The  animal  body  is  able  by  reduction  and  synthesis 
to  form  higher  organic  compounds  from  the  organic  food- 
stuffs. The  building  of  fats  from  carbohydrates  is  an  ex- 
ample of  a  well-proven  synthetical  reduction  taking  place  in 
the  animal  body. 

The  products  of  dissimilation  of  the  animal  world  can  be 
reassimilated  by  the  plants,  the  water  and  the  carbonic  acid 
directly,  but  the  ammonia  derivatives  only  after  they  have 
been  changed  to  nitrates  by  certain  Bacteria  found  in  the 
soil.  Thus  the  circulation  of  the  carbon,  hydrogen,  and 
nitrogen  in  the  organic  world  is  completed. 

For  the  physiological  combustion  a  continual  supply  of  free 
oxygen  is  not  necessary.  Frogs  can  live  for  a  long  time  in  an 
atmosphere  free  of  oxygen.  In  this  case  the  organism  obtains  the 
necessary  oxygen  from  the  oxygen  which  has  been  stored  up  in  its 
body  in  chemical  combination.  Many  organisms,  e.g.  anaerobic 
Bacteria,  can  generally  live  in  an  atmosphere  free  of  oxygen  and 
still  produce  carbon  dioxide,  obtaining  the  oxygen  from  surround- 
ing compounds  which  contain  this  element.  Unlike  the  intensity 
of  the  fire  in  a  furnace,  the  intensity  of  the  physiological  combus- 
tion cannot  be  increased  by  an  increased  supply  of  oxvgen. 

The  theory  of  the  transformation  of  energy  is  based  upon 
the  law  of  conservation  of  energy  discovered  by  J.  R.  Mayer 
and  H.  Helmholtz.  This  law  states  that  the  total  amount 
of  energy  in  the  universe  always  remains  constant,  that  no 


METABOLISM.     IRRITABILITY  3 

energy  is  created  or  destroyed,  and  that  energy  can  only 
change  from  one  form  to  another.  By  means  of  dissimila- 
tion the  stored-up  chemical  potential  energy  of  the  organic 
substance  is  changed  to  kinetic  energy,  mainly  to  heat  and 
mechanical  work,  and,  in  smaller  amounts,  to  electric  force 
(e.g.  in  the  electric  fishes)  and  light  (e.g.  in  fire-flies).  The 
kinetic  energy  set  free  by  dissimilation  enables  the  living 
body  to  perform  its  functions. 

By  assimilation  kinetic  energy  is  transformed  into  •chem- 
ical potential  energy  and  is  stored  up  in  the  organic  sub- 
stances. This  energy  is  derived  ultimately  from  the 
sunlight.  Only  in  the  presence  of  sunlight  are  plants 
containing  chlorophyll  able  to  assimilate.  For  assimilation 
not  all  the  light-rays  are  suitable,  only  the  red  and  yellow, 
not  the  green,  blue,  and  violet.  All  energy  which  enables 
the  living  being  to  perform  its  functions  is,  therefore,  sun- 
light changed  to  chemical  potential  energy. 

The  changes  of  matter  and  energy  in  the  living  being  can 
be  influenced  by  outside  chemical  and  physical  actions.  Of 
special  importance  are  the  influences  by  which  the  dissimila- 
tion is  increased.  Such  influences  are  called  stimulating 
agents  or  stimuli.  The  increased  dissimilation  brought 
about  by  the  stimulus  is  called  stimulation,  and  the 
resulting  activity  is  the  external  expression  of  the  stimula- 
tion. The  power  of  the  living  substance  to  respond  to  a 
stimulus  is  called  irritability. 

For  example:  A  muscle  stimulated  by  an  electric  current 
passes  from  the  condition  of  rest  into  the  condition  of  activity;  by 
it  the  processes  of  combustion  are  greatly  increased,  the  muscles 
shortened,  and  work  performed. 

The  stimulus  does  not  convey  to  the  stimulated  object 
the  energy  set  free  upon  stimulation,  but  only  calls  forth  the 
transformation  of  the  already  present  chemical  potential 
energy  into  kinetic  energy,  just  as  the  fuse  of  the  gun  calls 
forth  the  explosion  of  the  powder.  Hence  the  effect  of  the 
stimulation  is  not  proportional  to  the  stimulus. 

A   stimulation    produced    at  a  given  part  of  an  irritable 


4  HUMAN   PHYSIOLOGY 

structure,  e.g.  a  muscle-fibre,  can  spread  itself  throughout 
the  entire  structure  by  conduction. 

The  stimuli  are  classified  as: 

(i)  Chemical, — those  which,  by  means  of  chemical  action 
upon  the  irritable  substance,  cause  dissimilation.  Electrical 
stimuli  act  as  chemical  stimuli  because  the  current  produces, 
by  polarization  at  the  places  of  entrance  and  exit,  chemical 
changes  which  are  able  to  stimulate. 

(2)  Physical;  this  includes  mechanical  (hitting,  pulling) ; 
thermal  (heating)  and  photical  (light  which,  for  example, 
stimulates  the  retina).  The  action  of  these  physical  stimuli 
can  be  reduced  to  a  common  principle,  that  of  concussion, 
by  which  chemical  changes  producing  stimulation  are  called 
forth. 

Substances  which  can  be  decomposed  by  concussion  are  the 
explosive  bodies;  they  are  compounds  in  which  the  union  of  the 
atoms  is  unstable  and  which,  by  decomposition,  form  more  stable 
compounds.  The  irritable  substance  of  the  living  being  is,  per- 
haps, such  an  unstable  compound. 

Influences  which  decrease  the  amount  of  metabolism  are 
called  inhibitory  agents  and  their  effect  is  called  inhibition. 
The  condition  of  inhibition  in  which  the  vital  phenomena 
entirely  cease  without  the  power  of  life  being  destroyed  is 
called  latent  life  or  biostition.  In  biostition  there  are  many 
living  beings  at  the  lowest  temperatures  which  do  not 
destroy  life,  also  desiccated  seeds  of  plants,  spores  of 
Bacteria,  etc. 

Strong  stimulation  can  also  cause  inhibition,  which  is  then 
called  fatigue  or  exhaustion.  This  fatigue  is  due  to  the  excessive 
consumption  of  irritable  material  and  partly  to  the  harmful  effect 
of  the  dissimilation  products  (fatigue-substance)  retained  in  the 
irritable  structure.  A  fatigued  structure  at  rest  recovers  by  means 
of  the  reconstruction  of  the  irritable  substance  and  the  removal  of 
the  fatigue-substance. 


MORPHOLOGICAL    ELEMENTS   OF   THE  LINING   BEING  5 

2.  THE  PHYSIOLOGICAL  SIGNIFICANCE  OF  THE 
MORPHOLOGICAL  ELEMENTS  OF  THE  LIVING 
BEING 

The  characteristic  chemical  configuration  of  the  living- 
substance  is  connected  with  the  structure  or  organization  of 
the  living  being. 

The  structural  elements,  from  which  all  living  beings  are 
built  up,  are  called  cells.  The  characteristic  constituents 
of  each  cell  are : 

1.  The  protoplasm,  a  jelly-like  mass,  composed  of  a 
liquid  ground-substance  and  solid  constituents  (protoplasmic 
framework,  granules,  chromatophores,  and  other  inclosed 
objects) ; 

2.  One  or  more  nuclei  found  in  the  protoplasm,  generally 
spherical  bodies  composed  of  nuclear  framework,  nuclear 
sap,  nuclear  membrane,  and  nuclear  corpuscles. 

Protoplasm  and  nucleus  are  the  bearers  of  life. 

The  cells  which  compose  the  living  being  are  physiologi- 
cally of  very  different  value.  From  a  physiological  stand- 
point we  can  divide  them  into  two  groups: 

1.  Cells,  each  of  which  is  an  independent  living  being 
(physiological  individuals),  e.g.  all  unicellular  organisms 
(protists) ;  these  are  cells  which  possess  all  physiological 
activities  necessary  for  the  maintenance  of  life. 

Simpler  physiological  individuals  than  cells  are  not  known. 
Parts  of  cells  (separate  protoplasmic  masses,  single  nuclei)  are  not 
capable  of  independent  existence. 

2.  Cells  not  capable  of  existence  by  themselves,  but  only 
in  physiological  connection  with  other  cells,  for  in  them,  as 
in  the  members  of  an  organism,  some  physiological  processes 
are  strongly  developed,  while  others  are  more  or  less 
undeveloped  and  taken  up  by  cells  of  another  kind.  In  this 
case  many  cells  together  build  the  physiological  individual, 
and  the  processes  necessary  for  the  maintenance  of  life  are 
distributed  among  the  different  cells  of  the  individual.  As 
in  such  cells  the  specially  developed  physiological  processes 


6  HUMAN  PHYSIOLOGY 

appear  in  an  almost  pure  form,  they  are  physiologically  more 
simple,  but  for  this  reason  also  less  independent,  than  unicel- 
lular individuals. 

All  organisms  composed  of  many  physiologically  different 
cells  develop  from  undifferentiated  cells.  The  physiological 
differentiation  is  accompanied  by  a  morphological  differen- 
tiation, which  is  expressed  in  the  various  forms  of  the  cells. 

Although,  in  consequence  of  the  division  of  labor,  the 
various  kinds  of  cells  have  different  functions,  yet  those 
physiological  processes  which  are  connected  with  the  char- 
acteristic constituents  of  all  cells  must  be  common  to  all 
kinds  of  cells.  These  physiological  processes  include  in 
general  the  processes  which  belong  to  the  nourishment  and 
reproduction  of  the  cells.  These  processes  are  governed  by 
the  nucleus.  The  nucleus  of  the  reproductive  cells  is  the 
bearer  of  the  inheritable  qualities  of  the  organism. 

The  separation  of  the  living  substance  into  nucleus  and 
protoplasm  is  the  morphological  expression  of  the  physio- 
logical division  of  labor,  the  nucleus  being  predominantly 
concerned  with  the  nourishment  and  reproduction,  while  the 
protoplasm  chiefly  reacts  upon  external  influences. 

3.    GROWTH    AND    DEATH.       ORIGIN    AND    DEVELOP- 
MENT   OF    THE    LIVING    BEING 

If  in  a  living  being  assimilation  and  the  addition  of  assimi- 
lated products  predominate  over  dissimilation,  growth  of  the 
organism  results;  if  dissimilation  predominates,  the  body 
decreases.  In  each  organism  the  assimilation  predominates 
at  first,  the  body  grows;  later  on  the  activity  of  assimilation 
decreases,  the  body  begins  to  decrease,  and  this  results  in 
physiological  death  or  in  death  brought  on  by  senile  decay, 

A  new  living  being  originates  only  by  the  growing  and 
the  developing  of  a  part  separated  from  an  already  existing 
living  body.  This  part  grows  and  develops  into  a  new  living 
being  either  alone  or  after  the  union  with  a  part  of  a  second 
organism  of  the  same  kind.  Life  propagates  itself  from  the 
mother-  to  the  daughter-organism. 


ORIGIN  AND   DEVELOPMENT   OE   THE  LIVING   BEING  7 

Nothing  is  known  concerning  the  origin  of  the  first  living 
being  on  earth,  from  which  all  others  are  descendants. 

The  morphological  phenomena  of  growth  and  develop- 
ment of  a  living  being  are  the  increase  in  cells  and  the 
development  of  form. 

Cells  multiply  by  fission. 

In  this  process,  the  nucleus  is  divided  into  two  nuclei;  after 
this  the  protoplasm  divides  into  two  parts,  each  part  surrounding 
one  of  the  daughter-nuclei.  The  nuclear  division  is  either  direct 
by  the  fission  of  the  nucleus  or  indirect.  The  indirect  division 
takes  place  as  follows:  First  the  nuclear  framework  changes  to  a 
thick  skein-like  fibre;  this  fibre  divides,  by  transverse  section,  into 
a  number  of  segments,  and  each  segment  splits  longitudinally  into 
two  halves,  each  of  which  goes  to  build  up  one  of  the  daughter- 
nuclei.  In  this  indirect  nuclear  division,  the  centrosomes  have  a 
definite  influence.  These  structures  lying  in  the  protoplasm  near 
the  nucleus,  in  the  form  of  two  or  more  granules,  divide,  previous 
to  the  nuclear  division,  into  two  parts  and  these,  by  means  of 
fibrilles  which  proceed  from  them,  direct  the  course  of  the  separat- 
ing nuclear  segments.      (For  details  see  text-book  of  Histology.) 

The  formation  of  a  new  organism  results  in  one  of  two 
ways.  Either  some  cells  separated  from  the  mother  organ- 
ism by  cell  division  continue  to  exist  by  themselves  inde- 
pendently and  grow  (asexual  reproduction,  reproduction 
by  fission  or  budding) ;  or  two  cells,  derived  from  one  or 
two  sexually  different  living  beings  of  the  same  species,  unite 
to  form  one  living  being  (sexual  reproduction,  union  of  egg- 
and  sperm-cell). 

The  union  of  egg-cell  and  sperm-cell  is  the  fertilization. 
In  this  the  nuclei  of  the  cells  unite  into  one  nucleus.  By 
means  of  cell  division,  accompanied  by  cell  differentiation, 
the  new  organism  grows  from  the  fertilized  egg. 

In  many   species   of   living   beings    (e.g.    vascular   cryptogams, 

hydromedusa)  there  is  an  alternation  of  generation  in  which  one 

generation  propagates  itself  asexually,  and  the  other  sexually. 

t 

The  morphological  development  of  the  individual  organism 
(ontogeny)  results  in  the  development  of  the  daughter- 
organism,  derived  from  a  single  cell,  or  from  the  union  of 
egg-cell  and  sperm-cell,  into  a  form  similar  or  nearly  similar 


8  HUMAN  PHYSIOLOGY 

to  that  of  the  mother-organism.  The  mother-organism 
transmits  by  heredity  its  characteristics  to  the  daughter- 
organism. 

The  species  of  organisms  existing  at  present  have  not 
always  existed  since  the  beginning  of  life,  but  have,  in  the 
course  of  time,  been  developed  from  simpler  forms  of  life 
(development  of  species,  phylogeny). 

The  forms  which  the  growing  organism  assumes  during 
ontogeny  are  similar  to  the  forms  which  the  adults  possessed 
successively  during  the  phylogeny.  The  ontogeny  is  a 
short  recapitulation  of  the  phylogeny  (biogenetic  law  of 
Haeckel). 

The  cause  of  morphological  development  lies  in  the  vari- 
ability of  the  structure  and  functions  of  the  living  being,  i.e. 
in  the  quantitative  and  qualitative  variability  in  the  trans- 
formation of  energy  and  matter.  The  cause  of  this  variability 
is  not  known. 

The  principle  according  to  which  Darwin's  theory  of  selection 
explains  the  origin  of  species  on  the  ground  of  variability  is  the 
"  natural  selection  in  the  struggle  for  existence. "'  The  individuals 
of  a  generation  of  a  certain  species  differ  slightly  because  of  their 
variability  in  structure  and  functions.  Now,  the  struggle  for 
existence  which  the  individual  carries  on  with  hostile  beings  of 
the  same  or  other  species  is.  endured  best  by  those  individuals 
which  have  the  most  advantageous  characteristics.  These  indi- 
viduals are  therefore  sooner  selected  for  further  existence  and  for 
reproducing  offspring  which  inherit  their  characteristics.  Such  a 
selection,  carried  on  through  many  generations,  at  last  produces 
organisms  which  possess  that  characteristic  developed  to  such  an 
extent  that  they  really  differ  from  their  ancestral  organisms. 

The  continuous  selection  of  advantageous  variations  leads  to 
the  "development  of  beings  highly  fitted  for  their  environment. 
In  this  manner  originates  the  adaptation  which  we  see  in  so  many 
organs  and  organisms. 

While  the  Darwinian  theory  explains  the  origin  of  species  on 
the  basis  of  the  law  of  variability,  it  sheds  no  light  on  the  cause  of 
this  variability;  in  other  words,  it  does  not  explain  the  very  con- 
dition necessary  for  the  origin  of  species  and  therefore  cannot  be 
regarded  as  a  complete  explanation  of  phylogeny. 

The  principle  of  the  Darwinian  theory  is,  no  doubt,  applicable 
to  the  origin  of  many  species.      Whether  it  is  by  itself  a  sufficient 


CORPOREAL  LIFE  AND  SOUL   LIFE  9 

explanation  of  phytogeny,  or  whether,  besides  it,  external  or  in- 
ternal causes  are  active,  remains  a  question. 

According  to  another  theory  (Lamarckian),  any  influence  acting 
continually  upon  the  descendants  of  an  organism  so  as  to  produce 
the  same  changes  will  result  in  a  change  in  the  structure  and 
functions  of  the  organism,  and  this  change  is  inherited.  In  this 
manner  a  new  species  originates. 

Some  authors  assume  that  there  is  present  in  the  living  substance 
a  fixed  tendency  to  develop  and  perfect  itself. 


4.   CORPOREAL    LIFE    AND    SOUL    LIFE 

The  problem  of  Physiology  is  the  investigation  of  the 
objectively  demonstrable  processes  of  life.  Besides  these 
there  are  processes  which  can  be  perceived  subjectively  only. 
These  are  the  phenomena  of  soul  life,  the  conditions  and 
processes  of  consciousness.  The  investigation  of  soul  life  is 
the  province  of  Psychology. 

Psychical  processes  are  always  accompanied  by  and 
dependent  upon  physiological  processes  in  the  central 
nervous  system.  The  study  of  the  character  of  the  physio- 
logical processes  which  are  associated  with  the  psychical 
is,  of  course,  a  problem  of  Physiology.  Hence,  in  the 
study  of  the  central  nervous  system  and  sense-organs,  the 
physiologist  cannot  ignore  the  facts  of  psychology,  even 
though  it  is  not  his  aim  to  explain  the  psychical  phenomena. 

Corresponding  to  the  chief  phenomena  of  life  we  may 
divide  human  physiology  into  the  following  parts : 

i.    Metabolism. 

2.  The  transformation  and  setting  free  of  energy. 

3.  Reproduction  and  development. 


PART    I 

METABOLISM 

THE  combustible  constituents  of  our  body  continually 
undergo  chemical  changes,  in  that  they  are  burned  by  the 
inhaled  oxygen. 

The  products  of  combustion  are  removed  from  the  tissues, 
in  which  the  combustion  takes  place,  by  the  circulating 
blood  and  lymph;  one  of  these  products,  the  carbonic  acid 
gas,  is  excreted  from  the  body  by  the  lungs ;  the  other 
products,  by  glands. 

That  the  body  may  continue  to  exist,  new  material  for 
combustion  must  be  supplied  to  it  from  without.  This  is 
effected  by  the  partaking  of  nourishment  which  is  made 
absorbable  by  digestion,  and,  after  absorption,  supplied  to 
the  tissues  by  the  blood  and  then  assimilated. 

Metabolism,  therefore,  includes  the  following  parts  of 
physiology : 

i .  The  chemical  constituents  of  the  body  and  their  physio- 
logical importance. 

2.  Blood,  the  gases  of  the  blood  and  respiration,  circular 
tion  of  the  blood,  respiratory  movements,  lymph. 

3.  Secretions. 

4.  Nutrition,  alimentary  principles,  food,  digestion,  ab- 
sorption and  assimilation  of  the  digested  food. 

5.  Survey  of  metabolism  as  a  whole. 


CHAPTER    I 

CHEMICAL   COMPOSITION    OF   THE    HUMAN    BODY 

The  fifteen  elements  of  which  the  body  is  composed  are 
present  in  about  the  following  proportions: 

Carbon,         18.5$  Oxygen,  65. o# 

Hydrogen,   ii.ofo  Nitrogen,    2.5$ 

Sulphur,    Phosphorus,    Chlorine,    Iodine,     Fluorine,    Silicon, 

Potassium,    Sodium,    Calcium,    Magnesium,   Iron, — together 

lie 

The  adult  human  body  contains  about  3  g  iron.  Other  ele- 
ments, traces  of  which  are  sometimes  found,  must  be  regarded  as 
accidental  constituents. 

The  body  is,  therefore,  mainly  composed  of  non-metals 
(metalloids). 

Oxygen,  nitrogen,  and,  in  small  quantities,  hydrogen  are  the 
only  free  elements;  only  the  free  oxygen  is  of  physiological  im- 
portance. 

The  greater  part  of  these  anil  all  other  elements  are  found  in 
both  inorganic  and  organic  compounds,  in  which  they  take  the 
following  parts,  in  detail : 

1.  Carbon  forms  the  basis  of  all  the  organic  compounds  of  our 
body.  It  unites  with  hydrogen  and  oxygen  to  form  fats  and 
carbohydrates;  with  hydrogen,  oxygen,  nitrogen,  and  sulphur,  to 
form  proteid  bodies.  It  is,  therefore,  a  constituent  of  the  meta- 
bolic products  of  these  substances  and  this  chiefly  in  the  form  of 
carbonic  acid,  which  is  found  throughout  the  body,  partly  in  the 
free  state,  partly  in  the  carbonates  or  bicarbonates  of  the  alkalies 
and  calcium. 

2.  Hydrogen  is  mostly  (f)  united  with  oxygen,  forming  water. 
With  chlorine,  it  forms  hydrochloric  acid ;  with  sulphur,  sulphu- 
retted hydrogen,  found  in  the  intestinal  gases;  with  nitrogen, 
ammonia  and  its  salts.  Above  all,  it  is  one  of  the  chief  constitu- 
ents of  the  organic  compounds. 

3.  Nitrogen  appears  in  the  inorganic  compounds  only  as 
ammonia,  being  united  with  hydrogen.  It  is  found,  however,  in 
many  organic  compounds,  of  which  the  proteids  with  their  deriva- 
tives and  metabolic  products  are  the  most  important. 


CHEMICAL    COMPOSITION   OF   THE  HUMAN  BODY  13 

4.  Nine-tenths  of  the  oxygen  appears  in  the  form  of  water;  in 
small  proportions  it  is  present  in  carbonic,  sulphuric,  and  phos- 
phoric acids  and  their  salts.  Besides  this,  it  is  present  in  all  organic 
compounds  of  the  body  (except  in  a  few  hydrocarbons  in  the 
intestine). 

5.  A  small  part  of  the  sulphur  is  present  in  the  sulphates; 
another,  still  smaller  portion,  in  the  sulphuretted  hydrogen  and 
iron  sulphide  (intestine);  by  far  the  largest  part  is  found  in  the 
proteids,  where  it  appears  in  two  forms,  as  reduced  (easily  split  off 
by  boiling  with  alkali)  and  as  oxidized  (strongly  united  with  the 
proteid  molecule).  It  seems  to  be  present  in  bcth  forms  in  the 
metabolic  products  of  the  proteids. 

6.  Phosphorus  seems  to  be  present  in  inorganic  and  organic 
compounds  only  in  the  form  of  phosphoric  acid  which  forms  salts 
with  alkalies  and  calcium,  the  calcium  salt  forming  a  chief  con- 
stituent of  the  skeleton.  Organic  compounds  containing  phos- 
phorus are  lecithin,  jecorin,  protagon,  nuclein. 

7.  Iron,  deposited  as  inorganic,  i.e.  in  a  form  demonstrable  by 
the  ordinary  reactions,  in  the  liver  and  spleen  (probably  as  oxide), 
is  found  also  in  the  contents  of  the  intestine  (as  iron  sulphide). 
Of  special  physiological  interest  are  the  organic  iron  compounds, 
the  most  important  of  which  is  haemoglobin,  the  red  coloring 
matter  of  blood.  Many  nucleo-albumins  also  contain  a  little  iron. 
The  organic  compounds  of  iron  which  do  not  give  the  general  iron 
reactions  are  called  metal-organic  compounds. 

The  elements  thus  far  described  are  the  most  important  as  they 
are  the  organogenic  elements,  so  termed  because  they  form  the 
organic  substances  of  the  body. 

The.  other  four  elements  which  are  united  with  organic  sub- 
stances, especially  proteid  substances,  do  not  appear  in  metal- 
organic  compounds,  hence  it  is  concluded  that  these  elements  are 
present  in  the  organism  only  in  the  form  of  salts  or  inorganic  com- 
pounds. 

8  and  9.  Potassium  and  sodium,  in  about  equal  proportions, 
uniting  chiefly  with  carbonic,  hydrochloric,  and  phosphoric  acids, 
form  acid  and  neutral  salts.  Potassium  salts  predominate  in  the 
tissue-cells,  sodium  salts  in  the  tissue-fluids.  The  alkali-metals 
also  form  salt-like  bodies  with  the  proteids. 

10  and  n.  Calcium  and  magnesium,  as  the  salts  of  carbonic 
and  phosphoric  acids,  form  the  chief  constituents  of  the  bones. 
Calcium,  either  alone  or  with  phosphoric  acid,  is  also  united  with 
proteids. 

12.  Chlorine  is  present  as  free  hydrochloric  acid  (in  gastric 
juice) ;  or  united  with  an  alkali,  especially  sodium,  predominates 
in  the  tissue  fluids.  In  gastric  digestion,  hydrochloric  acid  forms 
acid  hvdrochlorates  with  the  products  of  proteid  digestion. 


14  HUMAN  PHYSIOLOGY 

13.  Iodine  is  found  in  thyroiodine,  a  substance  present  in  the 
thyroid  gland  of  adult  man. 

14.  Fluorine,  united  with  calcium,  is  present  in  the  enamel  of 
the  teeth. 

15.  Silicon  is  found  in  the  hair;  in  which  form  it  is  present  is 
not  known. 

The  chemical  compounds  found  in  the  body  may,  from  a 
physiological  standpoint,  be  divided  into  the  following 
groups : 

[.  Inorganic  compounds  (water  and  salts),  i.e.  saturated 
compounds  which  cannot  be  transformed  into  more  saturated 
compounds  by  chemical  processes  in  the  body  and,  hence, 
cannot  furnish  the  body  with  energy  for  its  functions.  Their 
importance  for  life  is  clue  to  their  physical  properties;  they 
also  take  part  in  chemical  actions,  but  no  utilizable  energy  is 
thereby  gained. 

2.  Organic  compounds  which  serve  as  sources  of  energy 
for  the  organism  (proteids,  fats,  carbohydrates) ;  the  stored-up 
chemical  energy  is  set  free  by  their  physiological  combus- 
tion. 

3.  Organic  compounds  which,  as  end-products  of  meta- 
bolism, are  formed  by  the  physiological  combustion  (nitrog- 
enous end-products  of  metabolism,  such  as  urea  and  others) 
and  are  destined  to  be  excreted  from  the  bod)-. 

1.   THE    INORGANIC    COMPOUNDS    OF  THE    BODY 

I.    Water  is  the   most  abundant  constituent  of  our  body, 

amounting  to  about  65$  of  the  body  weight  of  the  adult. 

In  new-born  children  the  proportion  of  water  is  above  yo/c 

The   following  table   indicates   the    amount  of  water  in   the 

different  tissues  and  organs: 

Adipose  tissue 15$  Pancreas 78$ 

Pones 50$  Blood 79$ 

Liver 70$  Lungs 79^ 

Skin 70$  Heart 79$ 

Spleen 77$  Kidneys 83$ 

Muscles 77$  Vitreous  humor 98.7^ 

Brain  and  spinal  cord.  78$  Cerebro-spinal  fluid..  .  99$ 


Intestine. 


/' 


CHEMICAL    COMPOSITION   OF   THE  HUMAN  BODY  15 

The  physiological  importance  of  water  is  as  follows : 

{a)  It  serves  as  a  solvent  and  as  such  it  renders  possible 
physical  and  chemical  processes  such  as  diffusion,  mechanical 
movement,  and  the  chemical  action  of  dissolved  substances. 

(b)  As  a  means  of  imbibition,  which  determines  the  semi- 
solid consistency  of  the  tissues. 

(r)  By  evaporation  from  the  lungs  and  body  surface,  it 
takes  heat  from  the  body  and,  hence  serves  as  a  tempera- 
ture regulator. 

(d)  It  takes  part  in  chemical  processes,  e.g.  in  the 
hydrolytic  splitting  up. 

2.  Bases  are  not  found  in  a  free  state  but,  united  with 
acids,  are  present  in  the  form  of  salts.  As  more  than  suffi- 
cient acids  are  present  for  the  union  with  bases,  acid  salts 
are  formed.  Under  certain  conditions  the  existence  of  a  free 
acid  must  be  granted,  namely,  carbonic  acid.  Hydro- 
chloric acid  is  found  in  a  free  state  in  the  gastric  juice ;  it  is 
set  free  from  sodium  chloride  by  the  gland-cell  of  the 
mucosa. 

3.  Salts,  formed  by  the  union  of  acids  and  bases,  in  which 
the  hydrogen  of  the  acid  is  replaced  by  the  metal  of  the 
base,  are  present  in  the  body  to  a  large  extent.  When  the 
tissue  is  burned  the  salts  remain  behind  as  ash.  The  ash, 
however,  is  not  identical  with  the  original  salts  of  the  body, 
as,  by  the  incineration  of  the  body,  substances  appear  in  the 
ash  which  were  not  present  in  that  form  in  the  organism. 
Originally  they  were  present  in  organic  compounds,  e.g. 
iron  as  a  constituent  of  haemoglobin ;  part  of  the  sulphuric 
and  phosphoric  acids  were  derived  from  the  proteid,  lecithin, 
and  nucleins.  On  the  other  hand,  certain  salts  originally 
present,  as  acid  carbonates  or  phosphates,  are  converted 
into  neutral  salts  by  combustion.  Very  often  the  salts  can 
be  investigated  only  after  the  incineration  of  the  tissue, 
therefore  the  ash  and  its  constituents  must  be  taken  into 
consideration  in  studying  the  composition  of  the  bod}'. 

The  amount  of  the  ash  of  the  body  is  about  5^  of  the  body 
weight,    of  which  the   skeleton  furnishes  over   80^  and  the 


1 6  HUMAN   PHYSIOLOGY 

muscles  io#  The  amount  of  ash  in  each  tissue  varies  much 
with  age  and  nourishment.  The  ash  percentage  of  tissues  is 
as  follows : 

Skeleton 22.0$  Heart 1.1$ 

Muscle 1.5$  Pancreas 1.0$ 

Liver 1.3$  Brain  and  spinal  cord.   i.of0 

Spleen 1.2$  Blood °-9$ 

Lungs i.ifc  Kidneys o.8fc 

Intestine 1. 1  fc  Skin 0.7$ 

The  ash  contains  (with  the  exception  of  iron  oxide)  only 
neutral  salts,  derived  from  the  bases  potassium,  sodium, 
calcium,  magesium,  and  from  carbonic,  sulphuric,  phosphoric, 
and  hydrochloric  acids.  More  than  80$  are  phosphates 
(chiefly  calcium  phosphate);  the  next  largest  in  quantity  arc 
the  chlorides  (sodium  chloridej ;  then  follow  the  carbonates 
and,  last  of  all,  the  sulphates. 

The  salts  of  potassium  and  sodium,  found  in  ash,  are 
soluble  in  water,  while  the  carbonate  and  phosphate  of 
calcium  and  magnesium,  iron  oxide  and  iron  phosphate  are 
insoluble  in  water.  In  the  body  fluid  the  carbonate  and 
phosphate  of  calcium  and  magnesium  are  acid  and  therefore 
soluble  in  water.  The  carbonates  of  the  alkalies  are  also 
present  in  the  body  as  acid  salts  (sodium  bicarbonate). 

When  two  or  more  salts  of  different  bases  or  acids  are  dissolved 
in  water,  they  exchange  their  components  reciprocally,  in  such  a 
manner  that  each  base  is  united  with  each  acid.  In  the  body 
fluid  there  are  four  bases  and  four  acids;  according  to  this  theory, 
sixteen  salts  ought  to  be  formed.  Moreover,  the  dibasic  sulphuric 
acid  and  carbonic  acid  form  two  salts  with  each  base,  while  the 
tribasic  phosphoric  acid  forms  three  salts  (the  primary,  secondary, 
and  tertiary  salts).  According  to  the  theory,  therefore,  many 
more  salts  must  be  formed.  The  quantity  of  each  salt  formed 
depends,  however,  upon  the  chemical  affinity  and  upon  the  abso- 
lute quantity  of  the  components  entering  into  the  reaction  (law 
of  mass  action).  Hence,  many  of  the  salts  formed  according  to 
the  theory  may  be  present  only  in  traces,  and  the  number  of  salts 
to  be  considered  is  much  reduced.  In  reviewing  the  salts  of  our 
body,  an  uncertainty  always  remains,  so  that  the  existence  of 
many  salts  is  not  absolutely  proved. 


CHEMICAL   COMPOSITION  OF   THE  HUMAN  BODY  17 

The  most  important  salts  of  the  body  are : 

1 .  Sodium  chloride  (common  table-salt).  This  is  chiefly 
found  in  the  fluids  of  the  tissues  (o.6<) ;  to  a  lesser  extent, 
in  the  cells.  It  serves  as  a  solvent  for  certain  proteids 
(globulin)  and  supplies  the  osmotic  pressure  of  the  body  fluid 
which  keeps  in  equilibrium  the  osmotic  pressure  of  the  cells. 
This  prevents  the  entering  of  water  into  the  cells.  In  pure 
water,  all  tissue  cells  die,  swelling  rapidly.  For  this  reason, 
in  the  investigations  of  living  tissue,  the  so-called  physio- 
logical salt  solution  (0.6$  NaCl)  is  used.  From  the  sodium 
chloride,  the  gastric  mucosa  forms  the  hydrochloric  acid  of 
the  gastric  juice. 

2.  Potassium  chloride  is  the  most  important  chlorine 
compound  in  the  cells  and  serves  to  maintain  the  osmotic 
equilibrium.  In  the  body  fluids  it  is  found  in  but  small 
quantities  and  is  not  of  any  special  physiological  significance. 

3.  Sodium  carbonate  is  chiefly  found  in  the  tissue  fluids 
(0.2-0.3$).  It  imparts  to  these  fluids  their  alkaline  reaction 
and  basic  nature. 

4.  Bicarbonate  of  sodium  is  also  found  in  the  tissue  fluids ; 
it  is  the  carrier  of  the  carbonic  acid  formed  by  combustion  in 
the  body.      (See  Chapter  III.) 

5.  Potassium  phosphate  (probably  the  secondary)  is  an 
important  constituent  of  all  cells.  It  is  the  most  abundant 
salt  in  the  cells.  It  is  doubtful  Avhether  the  salt  is  merely 
dissolved  in  the  fluids  of  the  cells  or  is  united  with  their 
organic  constituents. 

6.  Neutral  calcium  carbonate  forms  a  part  of  the  salts  of 
bones,  builds  the  otoliths  of  the  ear,  and  perhaps  also  the 
crystals  of  the  spermatic  fluid. 

7.  Acid  calcium  carbonate  is  dissolved  in  the  tissue  fluids. 
It  readily  yields  carbonic  acid  and  is  therefore,  like  bicarbon- 
ate of  sodium,  of  importance  as  a  carrier  of  carbon  dioxide 
in  the  exchange  of  gases  in  respiration. 

8.  Neutral  calcium  phosphate  is  the  chief  mineral  con- 
stituent of  the  skeleton,  of  which  it  forms  one-fifth  by  weight. 

9.  Acid    calcium    phosphate   is    dissolved   in    the   tissue 


1 8  HUM/IN   PHYSIOLOGY 

fluids.      In  the  coagulation  of  blood  it  is  supposed  to  aid  in 
the  formation  of  fibrin-ferment. 

10.  Magnesium  carbonate  and  magnesium  phosphate 
are  present  in  the  bones  and  often  accompany  the  calcium 
salts,  but  in  smaller  quantities.  Only  in  the  muscles  and  in 
the  thymus  does  the  magnesium  phosphate  exceed  the 
corresponding  calcium  salt. 

ii.  In  smaller  quantities  and  without  any  known  physiological 
importance  are  the  following:  Potassium  carbonate,  the  secondary 
sodium  phosphate,  sodium  sulphate,  potassium  sulphate,  magnesium 
sulphate,  calcium  fluoride  (in  bones  and  enamel  of  teeth). 

2.   THE  ORGANIC  ENERGY-YIELDING  COMPOUNDS  OF 

THE    BODY 

A  physiological  principle  according  to  which  the  following 
substances  maybe  grouped  is  not  yet  known,  as  our  knowl- 
edge of  the  role  of  each  one  in  metabolism  is  still  too 
limited.  We  may  classify  them  from  a  chemical  standpoint 
as  follows: 

i.    Carbohydrates;   2.  Fats;    3.  Proteids. 

1 .  The  carbohydrates  derive  their  name  from  the  fact 
that,  besides  carbon,  they  contain  hydrogen  and  oxygen  in 
the  same  proportion  as  water.  This  characteristic  has  no 
reference  to  the  chemical^  constitution  of  the  substances. 

The  carbohydrates  are  aldehydes  or  ketones  of  hexatomic 
alcohols  or  anhydrid  unions  of  two  or  more  molecules  of 
such  aldehydes  and  ketones.  Their  number  of  carbon 
atoms  is  six  or  a  multiple  of  six. 

Heating  changes  all  carbohydrates  to  caramel  having  a 
characteristic  odor ;  they  are  all  stained  red  by  thymol  and 
concentrated  sulphuric  acid. 

They  are  classified  as: 

Monosaccharides C,.H.„0 ..; 

Disaccharides C^H.^O,, ; 

Polysaccharides C(.HI(1Ov 

The  monosaccharides  and  disaccharides  are  also  called 
sugars;   they  have   a   more   or   less   sweet  taste,    the   disac- 


CHEMICAL    COMPOSITION   OF   THE  HUMAN  BODY  19 

charides  being  sweeter  than  the  monosaccharides.  Sugars 
are  soluble  in  water  and  alcohol,  but  insoluble  in  ether; 
they  crystallize  and  dialyze.  The  polysaccharides  are  in- 
soluble in  water  or  form  only  colloidal  solutions ;  they 
neither  crystallize  nor  dialyze. 

The  monosaccharides  (hexoses,  glucoses)  have  the  fol- 
lowing constitution : 

Aldehyde  sugar  (aldoses): 

CH2OH.CHOH.CHOH.CHOH.CHOH.C0H. 
Ketone  sugar  (ketoses) : 

CH2OH.CHOH.CHOH.CHOH.C0.CH2OH. 

Characteristics  of  monosaccharides : 

1.  They  are  optically  active,  i.e.  their  solutions  rotate 
the  plane  of  the  polarized  light ;  most  of  them  turn  it  to  the 
right;  only  fructose  turns  it  to  the  left  (hence  called  levu- 
lose).  The  optical  activity  of  the  sugar  is  due  to  the  pres- 
ence of  asymmetrical  carbon  atoms,  i.e.  carbon  atoms  whose 
four  valences  are  united  to  four  different  radicles  or  atoms. 

2.  The  aldehyde  sugars,  like  all  aldehydes,  are  easily 
oxidized,  forming  first  monobasic  and  then  dibasic  acids. 
The  ketoses  are  also  oxidized,  whereby  they  are,  at  the 
same  time,  split  up  into  bodies  containing  less  carbon. 
Upon  this  fact,  that  the  sugars  are  oxidizable,  depends  the 
detection  of  sugar  by  the  so-called  reduction  tests.  Of  these 
the  following  are  the  most  important: 

(a)  Trommer  s  test :  Sugar  solution  mixed  with  potassium 
hydrate  and  cupric  sulphate,  on  boiling,  gives  a  red  precipi- 
tate, the  cupric  oxide  having  been  reduced  to  the  insoluble 
cuprous  oxide. 

ib)  Bdttgcr  s  test:  Basic  bismuth  nitrate,  by  heating  with 
sugar  in  an  alkaline  solution,  is  reduced  to  metallic  bismuth 
(black  precipitate). 

{c)  Mulder' 's  test:  Weak  alkaline  indigo  solution,  heated 
with  sugar,  loses  its  color  through  reduction. 


20  HUMAN   PHYSIOLOGY 

3.  Moore's  test:  Roiled  with  alkali,  the  sugar  is  oxidized 
and  assumes  a  brown  color. 

4.  In  an  acetic  acid  solution,  monosaccharides,  like  alde- 
hydes and  ketones,  unite  with  phenylhydrazine,  forming 
hydrazones,  water  being  set  free.  This,  by  the  further 
taking  up  of  a  molecule  of  phenylhydrazine  and  the  separa- 
tion of  the  water  and  the  setting  free  of  hydrogen,  forms 
phenylosazone.  These  compounds  have  characteristic  crys- 
tals and  melting-points  which  may  aid  in  the  detection  of 
sugar. 

5.  Compounds  of  monosaccharides: 

(a)  Compounds  of  monosaccharides  with  bases  are 
called  saccharates.  Lead  saccharates  are  insoluble  in 
ammonia  and  are  therefore  used  for  the  precipitation 
of  sugar. 

(/))  Compounds  of  monosaccharides  with  alcohols, 
phenols,  aldehydes,  and  organic  acids  are  called  gluco- 
sides.  By  boiling  with  acids  or  by  the  action  of  main- 
ferments,  they  are  easily  decomposed,  under  the 
assumption  of  water,  into  their  components. 

6.  The  yeast-cell  splits  up  nearly  all  the  monosaccharides 
into  alcohol  and  carbonic  acid  (alcoholic  fermentation);  the 
bacterium  lactis  splits  up  most  of  them  into  lactic  acid  (lactic - 
acid  fermentation). 

Among  the  monosaccharides  are  grape-sugar,  fructose, 
galactose,  mannose.  Grape-sugar  is  found  in  the  animal 
body;   the  others  are  of  importance  as  foods. 

Grape-sugar  (glucose  in  a  more  restricted  sense,  or  dex- 
trose) is  the  aldehyde  of  sorbit,  a  hexatomic  alcohol  found 
in  the  service-berry. 

Grape-sugar  is  dextrorotatory  (hence  called  dextrose), 
reduces  and  forms,  with  phenylhydrazone,  phcnylglucosa- 
zone,  which  crystallizes  in  branches  having  the  melting- 
point  at  204  °  C.  It  is  capable  of  alcoholic  fermentation. 
Its  oxidation  forms  first  gluconic  acid  monobasic)  and  then 
saccharic  acid  (dibasic). 

Grape-sugar    is    found    in    sweet  fruits,    in   honey  and,    in 


CHEMICAL    COMPOSITION   OF    THE  HUMAN  BODY  21 

small  quantities,  in  the  blood  and  lymph.  It  is  the  form  in 
which  most  of  the  carbohydrates  in  the  body  are  carried  by 
the  blood  from  one  place  to  another  (from  intestine  to  the 
liver,  thence  to  the  tissues,  where  the  physiological  combus- 
tion takes  place).  Pathologically  it  appears,  often  very 
abundantly,  in  the  urine  (diabetes  mellitus). 

Glucosamin,  C  HuO.XH., ,  is  a  nitrogenous  derivative  of  grape- 
sugar  which  is  transformed  into  grape-sugar  by  the  action  of  nitric 
acid.  It  is  obtained  by  the  decomposition  of  chondroitin  (a  con- 
stituent of  cartilage)  or  of  chitin  (a  constituent  of  integuments  of 
arthropods).  This  transformation  is  of  importance  in  showing 
how  carbohydrates  can  be  derived  from  proteids. 

Inosit,  C6H120„ ,  a  sweet-tasting  substance,  does  not  belong  to  the 
sugars,  as  its  carbons  form  a  closed  circular  chain,  six  -CHOH— 
groups  forming  a  ring,  and  is  therefore  hexahydroxy-benzene. 
Inosit  is  soluble  in  water,  insoluble  in  alcohol  and  ether,  optically 
inactive,  does  not  reduce  nor  ferment  with  yeast,  but  undergoes 
lactic-acid  fermentation.  It  crystallizes  in  prisms,  grouped  in 
rosettes.  Successively  treated  with  nitric  acid,  ammonia,  and 
calcium  chloride,  it  leaves,  on  drying,  a  rose-red  spot.  Inosit  is 
found  in  muscles;  its  physiological  importance  is  unknown. 

Disaccharides  are  anhydrid  compounds  of  two  monosac- 
charide molecules  of  the  same  or  different  kinds: 

2(C6H1206)2-H20  =  C12H22On. 

In  this  group  belong: 

Cane-sugar  =  grape-sugar  -f-  fructose. 

Milk-sugar  (lactose)  =  grape-sugar  -|-  galactose. 
Maltose  =  grape-sugar  -(-  grape-sugar. 

By  boiling  with  acids  and  by  inverting  ferments,  these 
sugars,  under  the  assumption  of  water,  are  split  up  into  their 
components.  They  are  dextrorotatory,  reduce  (except 
cane-sugar)  and  form  phenylosazones.  Lactosazone  melts 
at  200°;  maltosazone  at  2080.  The  disaccharides  do  not 
undergo  alcoholic  fermentation  directly. 

Cane-sugar  and  maltose  are  important  foods.  Lactose  is 
also  an  important  food  and  is  of  special  physiological  interest 
because  it  is  a  specific   product  of  the  animal   body,  being 


22  HUMAN   PHYSIOLOGY 

formed  by  the  activity  of  the  milk-glands.  It  is  found  only 
in  milk,  has  but  a  slight  sweet  taste,  and  is  somewhat  less 
soluble  in  water  than  the  other  sugars.  Milk-sugar  is 
dextrorotatory  (rotatory  power  52. 50).  It  reduces,  but 
does  not  ferment  with  yeast,  even  after  previous  action  of 
the  invertin,  which  otherwise  splits  up  the  disaccharides  and 
renders  the  yeast  fermentation  possible.  On  the  other 
hand,  it  is  split  up  by  bacterium  lactis  (lactic-acid  fermenta- 
tion), also  by  the  Kephir  fungus,  which  also  produces  alco- 
holic fermentation.  Through  the  oxidation  of  milk-sugar 
there  is  formed,  among  others,  mucic  acid,  an  oxidation 
product  of  galactose. 

The  polysaccharides  are  anhydrid  compounds  of  several 
molecules  of  the  simple  sugars.  Their  general  formula  is 
(C6H10O5)jt,  in  which  x  is  the  still  unknown  factor  by  which 
the  formula  must  be  multiplied  to  obtain  the  real  size  of  the 
molecule.  In  this  group  belong:  vegetable  starch  (anky- 
loses), animal  starch  (glycogen),  dextrin,  gums,  and  cellu- 
lose. Some  of  the  polysaccharides  are  insoluble  in  water 
(cellulose);  some  swell  up  in  water,  forming  a  sticky  fluid, 
(starch,  gums) ;  some  are  soluble,  but  are  not  dialyzable, 
and  are  precipitated  by  alcohol  (glycogen,  dextrin).  They 
are  dextrorotatory,  do  not  reduce  (except  a  few  dextrins), 
and  do  not  ferment  with  yeast.  Many  ferments  (diastase, 
ptyalin)  and  boiling  with  strong  mineral  acids  change  the 
monosaccharides,  chiefly  to  grape-sugar.  When  gum  is 
oxidized,  mucic  acid  is  formed;  the  oxidation  of  starch, 
glycogen,  dextrin,  yields  saccharic  acid.  Most  of  the  poly- 
saccharides give  color  reaction  with  iodine:  Starch  gives 
blue;  glycogen,  brownish  red;  dextrin,  blue  or  red;  cellu- 
lose, after  being  treated  with  concentrated  sulphuric  acid, 
gives  blue. 

Of  the  polysaccharides,  only  glycogen  is  found  in  the 
animal  body. 

Cellulose  is  the  chief  constituent  of  wood  fibre.  Starch  and 
dextrin  are  important  foods.  Gum  has  only  a  technical  value. 
A    carbohydrate,    closely   related    to    cellulose,    is    found    in    the 


CHEMICAL    COMPOSITION   OF   THE  HUMAN  BODY  23 

envelopes  of  the  Tunicates.  A  gum-like  carbohydrate  can  be  split 
off  from  certain  mucins  (animal  gum). 

Glycogen  is  chiefly  found  in  the  liver  and  muscles.  It  is 
formed,  first  of  all,  by  the  anhydrid  union  of  several  mole- 
cules of  the  simple  sugar,  chiefly  of  dextrose,  but  also  of 
levulose  and  galactose.  Glycogen  can  also  be  formed  from 
proteid. 

Glycogen  is  dextrorotatory;  boiling  with  acids  splits  it  up 
into  dextrose  only,  hence  in  the  formation  of  glycogen  from 
levulose  and  galactose,  these  must  first  be  changed  to  dex- 
trose. 

Glycogen  forms  an  opalescent  solution  in  water  and  is 
precipitated  by  the  addition  of  half  its  volume  of  alcohol. 
It  dqes  not  reduce  nor  ferment  and,  with  iodine  potassium 
iodide,  gives  a  brownish-red  color  which  disappears  on  heat- 
ing. Ferments  (diastase,  ptyalin)  split  it  up,  under  the 
assumption  of  water,  into  maltose  and  dextrose,  dextrins 
being  intermediate  products. 

The  object  of  glycogen  formation  in  the  animal  body  is 
the  storing  up  of  carbohydrates  in  a  form  which,  under  the 
given  conditions,  is  insoluble  (like  the  sugar  in  plants  is 
stored  up  as  starch). 

2.  Fats  are  fatty  acid  esters  of  glycerin.  The  most  im- 
portant fatty  acids  which  take  part  in  ester  formation  are : 

Palmitic  acid,  C15H31COOH; 
Stearic  acid,  C^H3.COOH; 
Oleic  acid,         C^H^COOH. 

Glycerin  as  a  triatomic  alcohol  can  unite  with  three  mole- 
cules of  fatty  acid : 

/0H  /0(C16H310) 

C3H-OH  -f  3C15H31COOH  =  C3H -0(C16H310)  +  3H,0. 
\OH  \0(C16H310) 

The  glycerin-esters  of  palmitic,  oleic,  and  stearic  acids  are 
called  palmitin,  olein,  and  stearin,  and  a  mixture  of  these 
three  is  what  is  commonly  known  as  fat. 

The  melting-point  of  stearin  is  71.  50,  of  palmatin  62°,  of 


24  HUMAN   PHYSIOLOGY 

olein  0°.  According-  to  the  proportion  of  stearin  and  palma- 
tin  on  the  one  hand  and  olein  on  the  other,  the  natural  fats 
are  solid  at  ordinary  temperature,  as  tallow  and  butter,  or 
liquid,  in  which  condition  they  are  called  oils. 

In  small  quantities  there  are  present  in  animal  fats  the  glycerides 
of  butyric  acid,  C4H802 ,  caproic  acid,  C6H1202,  caprylic  acid, 
CH1602,  capric  acid,  C'1(1H.,(|(), ,  and  myristic  acid,  C34H2802. 

Fats  are  insoluble  in  water  and  cold  alcohol,  but  readily 
soluble  in  hot  alcohol  and  in  ether.  Stearin  and  palmitin 
solidify  in  needle-shaped  crystals.  On  heating,  especially 
with  the  anhydrid  of  phosphoric  acid,  the  fats,  in  contra- 
distinction from  free  fatty  acids,  yield  the  offensive-smelling 
acrolein,  a  decomposition  product  of  glycerin.  The  fats  are 
stained  black  by  osmic  acid.  By  boiling  with  alkalies, 
especially  in  alcoholic  solutions,  also  by  the  action  of  many 
ferments  (steapsin  of  the  pancreatic  juice)  they  are  split  up, 
under  the  assumption  of  water  into  glycerin  and  free  fatty 
acids.  The  fatty  acids  unite  with  the  alkali  present,  forming 
salts  of  fatty  acids,  the  soaps  (sodium  soap  or  hard  soap, 
potassium  soap  or  soft  soap). 

If  the  fats  contain  free  fatty  acid  (rancid  fats),  they  can, 
on  melting,  form  an  emulsion  with  water  and  a  little  soda; 
in  this  process  of  emulsion  the  fats  are  finely  divided,  forming 
a  milky  fluid.  As  emulsification  is  dependent  upon  the 
presence  of  soap,  formed  by  the  union  of  fatty  acid  and 
alkali,  a  purely  neutral  fat  cannot  be  emulsified.  The 
emulsification  of  fat  is  of  importance  in  the  absorption  of  fat 
in  the  food. 

Fats  are  found  in  all  parts  of  the  body,  generally  stored 
up  in  cells.  The  percentage  of  fat  in  the  tissues  varies  very 
much,  as  it  is  dependent  upon  the  state  of  nutrition.  In 
lean  meat  there  is  but  little  above  \%  fat,  while  the  quantity 
of  fat  in  a  fattened  animal  may  be  above  30$.  The  tissues 
containing  the  most  fat  are  the  subcutaneous  tissue,  the 
mesentery,  the  bone  marrow  (adipose  tissue),  which  may  con- 
tain about  80^  fat. 


CHEMICAL    COMPOSITION   OF   THE  HUMAN   BODY  25 

The  physiological  functions  of  fat  are : 

(a)  By  their  physiological  combustion  the}'  are  a  source 
of  heat  and  force. 

(p)  Being  poor  conductors  of  heat,  they  shield  the  body 
from  rapid  cooling. 

(<r)  They  serve  as  protective  coverings  for  delicate  organs 
(eyes,  kidneys). 

Cholesterins  are  isomeric  monatomic  alcohols  of  unknown 
constitution,  having  the  empirical  formula  C0(.H  (OH). 
They  crystallize  in  rhomboid  tables,  are  insoluble  in  water, 
but  readily  soluble  in  hot  alcohol  and  ether.  Moistened 
with  concentrated  sulphuric  acid  and  a  little  iodine  solution, 
the  cholesterin  crystals  become  blue,  green,  and  red.  A 
solution  of  it  in  chloroform  is  colored  blood-red  by  concen- 
trated sulphuric  acid.  Cholesterins  are  found  in  all  parts  of 
the  organism,  chiefly  in  the  brain  and  nerves,  also  in  the 
bile.  With  fatty  acids  they  form  esters,  capable  of  saponifi- 
cation with  alkali  and  found  in  small  quantities  throughout 
the  whole  body.  The  physiological  function  of  cholesterin 
is  not  known;  its  ester  (lanolin)  protects  the  skin  and  hairs, 
for  which,  as  it  does  not  become  rancid,  it  is  well  adapted. 

Lecithins  are  ester-like  compounds  of  glycero-phosphoric 
acid  with  two  fatty  acid  radicles  on  the  one  hand  and  of  an 
ammonia  base,  cholin,  on  the  other.  Cholin  is  trimethyl- 
oxyethyl-ammonium-hydroxide.  From  cholin  we  obtain, 
by  reduction,  rieurin,  and  by  oxidation,  muscarin.  Neurin 
and  muscarin  are  poisons,  cholin  is  not. 

The  most  common  lecithin,  stearic  acid  lecithin,  is  di- 
stearyl-glycero  -  phosphoric  acid  trimethyl  -  oxyethyl  -  am- 
monium-hydroxide : 

/0-C18HrO 

C3H.— 0-C18H3!o 

\0       /OH 

xO.C,H4.N<^5> 

VLH3 

\OH. 
Lecithin  is  insoluble  but  swells  up  in  water,  forming  the 


26  HUMAN  PHYSIOLOGY 

so-called  myelin  figures.      It  is  soluble  in  ether  and  alcohol, 
has  the  consistency  of  wax  and  yields  imperfect  crystals  only 
at  a  very  low  temperature.      Boiled  with  acids  and  alkalies, 
*it  splits  up  into  fatty  acid,  phosphoric  acid  and  cholin. 

Lecithin,  no  doubt  partly  united  with  proteid,  is  a  con- 
stituent of  all  animal  cells.  It  is  present  in  large  quantities 
in  the  brain,  spinal  cord,  and  yolk  of  birds'  eggs. 

Proiagon,  a  substance  containing  phosphorus  and  nitrogen 
(constitution  unknown),  is  a  constituent  of  nerves  and  yields 
similar  decomposition  products  as  lecithin.  It  can  be  extracted 
from  the  brain  by  85$  cold  or  45$  warm  alcohol  and  is  thrown 
down  as  crystals  when  cooled  to  o°.  It  swells  up  in  water,  form- 
ing an  opalescent  solution  and  is  soluble  only  in  warm  alcohol  and 
in  ether.  At  50°  C.  it  is  decomposed,  giving  rise  to  the  following 
glucoside-like  cerebrins  free  from  phosphorus:  cerebrin,  homocere- 
brin,  encaphalin.  The  cerebrins,  boiled  with  dilute  sulphuric 
acid,  yield  galactose  and  a  fat  called  cetylid. 

/(■coriu,  a  glucoside-like  body  containing  phosphorus,  appears 
to  be  related  to  protagon.  It  is  found  in  the  liver  and  other 
organs. 

The  physiological  significance  of  these  substances  is  not  known. 

To  the  fatty  bodies  also  belong  a  few  coloring  compounds, 
stored  up  in  the  body  as  pigments,  called  chromophane  and  lipo- 
chrome. 

3.  Proteids. — The  term  proteid  is  here  used  in  its  widest 
sense;  it  also  includes  the  proteid-like  bodies  (albuminoids) 
which  are  not  regarded  as  real  proteids  by  man)-  authors. 

{a)   Composition  of  Proteids. 

Proteids  all  contain:  carbon  50-55$,  hydrogen  6.5-7.3$, 
nitrogen  15-17$,  oxygen   19-24'J,  sulphur  0. 3-2.4$. 

besides  these,  there  are  present  phosphorus,  iron,  calcium,  mag- 
nesium, potassium  and  sodium;  but  these  are  not  necessary  con- 
stituents of  proteids,  for  they  are  united,  either  alone  or  with  other 
elements,  to  the  already  independent  proteid  molecule. 

Nearly  all  proteid  bodies  contain  a  small  amount  ol  mineral 
constituents  which,  on  incineration,  remain  behind  as  the  ash. 
These  are  not  present  as  impurities,  but  are  chemically  united  with 
the  proteid. 

Nothing  is  known  for  certain  about  the  constitution,  molecular 
weight,  and  empirical  formula  of  proteid.  It  is  certain  that  the 
proteid  molecule  is  very  large. 


CHEMICAL    COMPOSITION  OF   THE  HUMAN  BODY  27 

The  most  reliable  statements  on  this  subject  are  concerning 
the  crystallized  serum  albumin  of  the  horse,  which  is  supposed  to 
have  a  molecular  weight  of  17,070  and  the  empirical  formula 
"C,..H,„.N,„-S,„0.„..      This  number  is  calculated  from   the  amount 

OD        1210      19a     10      2.5.0  * 

of  sulphur       The  sulphur  of  most  proteids  exists  in  two  forms: 

1.  Easily  split  off  by  hot  alkali ;  with  lead  acetate  it  forms  lead  sul- 
phide :  reduced  sulphur. 

2.  Firmly  bound  to  the  proieid  molecule,  only  demonstrable  as  sul- 
phuric acid  after  the  decomposition  of  the  proteid :  oxidized  sulphur. 

Such  proteids  must  contain  at  least  two  atoms  of  sulphur. 

In  serum  albumin  the  proportion  between  the  firmly  and  the 
loosely  combined  sulphur  is  as  2:3:  the  molecule,  therefore, 
contains  at  least  five  atoms  of  sulphur.  This  number  must  be 
•doubled  as  the  serum  albumin  splits  up  into  at  least  seven  diges- 
tion-products which  contain  sulphur;  of  these,  three  contain 
.sulphur  in  both  forms.  With  ten  atoms  of  sulphur  in  the  mole- 
cule the  calculations  from  the  elementary  composition  [C  = 
53.08^;  H  =  7.12^;  X  =  15.93^;  S  =  1.875^;  O  =  21.995$] 
furnish  us  with  the  above  formula.  According  to  the  method  of 
•determining  the  freezing-point,    the  molecular  weight   of    15,00.0 


(h)    The  Decomposition  Products  of  Proteids. 

By  boiling  with  alkalies  or  acids  and  by  putrefaction,  proteids 
.are  decomposed.      The  decomposition  products  are: 

1.  If  the  decomposition  is  long  continued:  ammonia,  carbon 
dioxide,  acetic  acid,  oxalic  acid,  phenol,  indol,  skatol. 

2.  If  the  decomposition  is  not  continued  for  a  long  time:  amido 
acids  and  hexo-bases. 

The  following  are  the  most  important  amido  acids  : 

Glycocoll,  amidoacetic  acid,  XH„.  CH2.COOH,  is  found  chiefly 
among  the  decomposition  products  of  gelatin. 

Leucin,  amidocaproic  acid,  C1H9.C*H(XH:,).COOH,  crystallizes 
in  radially  striated  spheres. 

Tyrosin,  oxyphenol-amidopropionic  acid, 

OH.C6H4.CH2.CH(NH2).COOH, 

crvstallizes  in  rosette-like   clusters  and  is   colored   red  by  million's 
fluid. 

Aspartic  acid,  amidosuccinic  acid, 

COOH.  CH2.  CH(XH.,).  COOH, 

is  extensively  found  as  the  amid  (asparagin),  in  plants. 

The  Hexo-bases,  lysine,  arginine,  and  histidine,  are  nitrogenous 
substances    having    strong    basic    properties,    and    containing   six 


28  HUMAN  PHYSIOLOGY 

atoms  of  carbon  in  each  molecule.  Some  substances,  containing 
no  sulphur,  are  composed  of  hexo-bases  and  gi\e  real  proteid 
reactions.  These  substances  are  therefore  regarded  as  the  simplest 
proteids  and  are  called  protamine.  From  arginme  urea  may  be 
obtained  by  boiling  with  baryta  water,  proving  that  urea  may  be 
formed  from  proteids  by  a  simple  process  of  splitting  up. 

By  means  of  putrefaction,  other  products  may  also  be  formed 
which  are  not  simple  decomposition  products  of  the  proteid,  but 
which  must  be  regarded  as  metabolic  products  of  the  bacteria, 
causing  the  putrefaction.  These  products  are  called  ptomains, 
some  of  which  are  very  poisonous. 

Potassium-permanganate  oxidizes  proteids  to  oxyprotosulphonic 
acid,  which  has  still  the  character  of  a  proteid  but  contains  more 
oxygen  and  the  sulphur  in  a  completely  oxidized  form. 

Because  of  their  decomposition  products  and  their  relation 
to  acids  and  bases  with  which  they  form  salt-like  combina- 
tions, the  proteids  may  be  considered  as  condensation 
products  ofVarious,  in  part  aromatic,  amido  acids.  Otherwise 
nothing  is  known  as  to  their  chemical  constitution. 

if)  Physical  Properties  of  Proteids. 

Most  proteids  are  soluble  in  water  or  dilute  salt  solutions, 
but  insoluble  in  alcohol  and  ether. 

They  arc  levorotatory. 

They  dialyze  (except  peptone)  with  difficulty  or  not  at  all 
through  animal  and  vegetable  membranes. 

The)'  do  not  readily  crystallize.  Crystals  have,  however, 
been  obtained  from  haemoglobin,  vitellin,  egg  and  serum 
albumin,  and  from  many  vegetable  proteids. 

The  fact  that  crystallizable  proteids  do  not  dialyze  contradicts 
the  old  classification  of  crystalloid  and  colloid  bodies  (although 
this  had  already  been  proven  untenable).  Proteids  do  not  dialyze 
because  their  molecules  are  too  large  for  the  pores  of  the  mem- 
branes. 

id)  Reactions  of  Proteids. 

A.  Precipitants  of  proteids. 

i.  Many  proteids  are  rendered  insoluble  by  heat:  they 
coagulate. 

The  coagulation  temperature  lies  between  50°  and  8o°.  The 
exact  temperature  does  not  only  depend  on  the  nature  of  the 
proteid  but  also  on  the  concentration,  the  amount  of  salts  present, 


CHEMICAL    COMPOSITION   OF    THE  HUMAN   BODY  29 

and   the  reaction   of  the  solution.      In   strongly  acid   or  alkaline 
solutions,  coagulation  does  not  occur. 

The  coagulation  does  not  produce  any  real  change  in  the  nature 
of  the  proteid ;  probably  only  an  anhydrid  condensation  or  poly- 
merization takes  place.  Coagulated  proteid  contains  less  ash  than 
non-coagulated  proteid;  hence  by  coagulation  a  part  of  the 
mineral  constituents  of  the  proteid  is  split  off. 

2.  Many  proteids  are  precipitated  by  alcohol.  If  the 
action  of  the  alcohol  is  allowed  to  continue,  the  precipitated 
proteid  is  coagulated. 

3.  Nearly  all  proteids  are  precipitated  by  saturating  their 
solutions  with  neutral  salts  (sodium  chloride,  magnesium, 
sodium,  and  especially  ammonium  sulphatej.  An  acid 
reaction  favors  this  precipitation. 

The  precipitation  by  salts  is  first  of  all  due  to  the  fact  that  the 
salts  deprive  the  proteid  of  the  solvent.  Still,  chemical  action 
is  not  excluded.  In  using  ammonium  sulphate,  for  example, 
ammonia  is  set  free,  for  the  sulphuric  acid  unites  with  the  precipi- 
tated proteid  and  at  last  causes  a  splitting  up  of  the  proteid. 

By  precipitation  by  salts,  proteids  can  be  obtained  in  crystalline 
form.  Proteids  cannot,  like  other  substances,  be  crystallized  bv 
mere  evaporation  of  the  water  which  holds  them  in  solution,  for, 
in  proportion  as  the  water  is  evaporated,  the  proteids  are  precipi- 
tated and  form  a  solid  pellicle  at  the  surface  of  the  water.  Hence 
the  solution  does  not  reach  the  condition  pf  supersaturation 
necessary  for  crystallization.  This  can,  however,  be  "obtained  by 
using  salt  as  a  precipitant,  whereby  the  concentration  of  the  salt 
is  gradually  increased  either  by  the  careful  addition  of  the  salt  to 
the  solution  or  by  evaporation.  For  this  purpose,  sodium  or 
ammonium  sulphate  is  best. 

4.  Proteids  are  precipitated  by  concentrated  mineral  acids, 
especially  by  nitric  acid  (Heller's  test).  Metaphosphoric 
acid  readily  precipitates  proteids,  while  the  orthophosphoric 
acid  does  so  with  difficulty. 

5.  Proteids  are  precipitated  by  the  salts  of  the  heavy 
metals,  copper  sulphate,  ferric  chloride,  neutral  and  basic 
lead  acetate,  platinum  chloride,  corrosive  sublimate  in  hydro- 
chloric acid  solution.  In  these,  the  heavy  metals  unite  with 
the  proteids  as  a  weak  acid,  forming  a  compound  insoluble 
in  water. 


3°  HUMAN  PHYSIOLOGY 

6.  Proteids  are  precipitated  by  some  weak  organic  acids 
or  their  salts  in  a  solution  of  acetic  acid:  hydroferrocyanic 
acid,  potassium  ferrocyanide  and  acetic  acid,  tannic  acid, 
picric  acid,  trichloracetic  acid.  In  this  case  also  compounds 
insoluble  in  water  are  formed,  in  which  the  proteids  seem  to 
take  the  part  of  a  base. 

7.  Proteids  are  also  precipitated  by  phosphotungstic  and 
phosphomolybdic  acids  and  potassio-mercuric  iodide  in  the 
presence  of  free  hydrochloric  acid. 

B.   Color  reactions  of  proteids. 

1.  Xanthoproteic  reaction.  Proteids  boiled  with  strong 
nitric  acid  turn  yellow,  which  is  colored  orange  by  ammonia. 

2.  Mi/ion's  reaction.  Proteids  boiled  with  mercuric 
nitrate  solution  containing  excess  of  nitric  acid  are  colored 
brick-red.  This  coloration  depends  upon  the  oxyphem  1 
nucleus  of  the  proteids  (as  in  case  of  tyrosin). 

3.  Biuret  reaction.  If  to  a  solution  of  proteid,  sodium 
hydrate  and  dilute  copper  sulphate  be  added,  a  violet  or 
rose-red  color  results.  Biuret,  a  derivative  of  urea,  also 
gives  this  reaction. 

4.  Adamkiewicz^  reaction.  To  a  solution  of  proteids  in 
acetic  acid,  add  excess  of  concentrated  sulphuric  acid.  A 
reddish-violet  color  appears. 

(y)  Physiological  Importance  of  Proteids. 

The  albuminous  bodies  are  the  most  important  constitu- 
ents of  our  bod)-,  for  all  tissues  and  organs  are  composed 
of  them.  Hence  they  are  also  called  the  proteids  (from 
npoDTevoo).  They  form  the  chemical  and  physical  basis  of 
the  living  substance  and  are  present  in  the  body  partly  in  a 
solution,  e.g.  the  tissue  fluids  and  cell  saps;  partly  in  a  solid 
form  (more  or  less  swollen  >,  forming  the  cells  and  tissues. 

The  proteids  (including  the  albuminoids)  form  about  one 
sixth  of  the  bod}- weight.  About  one  half  of  all  the  proteids 
of  the  body  are  contained  in  the  muscles,  which  are  composed 
of  about  20-;  proteids.  The  liver,  spleen,  and  blood  also 
contain  the  same  percentage  of  proteid.      The  nerves,  brain. 


CHEMICAL    COMPOSITION   OF    THE  HUMAN   BODY  3T 

and  spinal  cord  have  comparatively  less  proteids,  only  8/B. 
The  bones  contain  14$  (mostly  collagen);  the  skin  contains 
24^  (mostly  collagen) ;  the  adipose  tissue  contains  only  a 
small  amount  (hardly  3^)  of  proteids. 

(_/")    Classification  of  Proteids. 

Proteids  are  classified  into:  1.  Albuminous  bodies  or 
simple  proteids;  2.  Combined  proteids;  3.  Proteoses;  4. 
Albuminoids. 

I.  Albuminous  bodies  or  simple  proteids  are  the  proteids 
in  a  more  restricted  sense  of  the  word  (native  proteids)  as 
they  are  found  in  the  albumin  (white)  of  the  egg.  They  are 
soluble  in  water  or  in  dilute  salt  solutions,  are  levorotatory 
and  give  all  the  precipitations  and  color  reactions. 

In  this  class  belong  the  albumins  and  globulins.  The 
albumins  contain  more  sulphur  and  give  a  weaker  xantho- 
proteic reaction  than  the  globulins. 

The  albumins  are  soluble  in  water ;  most  of  the  globulins- 
are  soluble  only  in  a  dilute  salt  solution.  The  globulins  are 
therefore  precipitated  by  half  saturation  with  ammonium  sul- 
phate or  by  complete  saturation  with  magnesium  sulphate. 
The  albumins  are  not  so  precipitated.  The  globulins,  in 
distinction  from  the  albumins,  are  precipitated  from  their 
solution  by  very  dilute  acids,  even  by  carbonic  acid. 

Among  the  albumins  there  are  serum  albumin,  egg  albumin,  lact 
albumin,  muscle  albumin.      These  albumins  differ  in  their  solubility, 
coagulation  temperature,  and  in  their  specific  rotatory  power. 

Among  the  globulins  we  have  serum  globulin,  egg  globulin,  fibrin- 
ogen, myosinogen.  From  fibrinogen,  a  constituent  of  the  plasma, 
the  insoluble  fibrin,  is  formed  by  the  action  of  the  fibrin  ferment. 
Myosinogen,  a  constituent  of  muscles,  coagulates  during  rigor 
mortis,  yielding  the  myosin.  The  yolk  of  egg  also  contains  a 
globulin-like  body,  vitellin. 

With  acids  and  alkalies,  the  simple  proteids  form  syntonin 
(acid  albumin)  and  alkali  albumin.  These  are  not  coagulated 
by  heat  and  are  precipitated  by  neutralizing  their  solutions. 


3-'  HUMAN   PHYSIOLOGY 

Syntonin,  alkali  albumin,  and  coagulated  egg  albumin  are  also 
called  derived  albumins,  in  distinction  from  the  native  albumins. 

The  simple  proteids  of  our  body  are  chiefly  dissolved 
in  the  blood,  lymph,  and  serous  fluids,  and  form  the 
material  for  replacing  the  proteid  wastes  in  the  tissues. 
For  this  purpose,  these  proteids  are  continually  circulated 
through  the  body  by  means  of  the  blood  and  lymph  and  are 
therefore  called  circulating  proteids,  in  distinction  from  the 
deposited  organ  proteids.  The  circulating  proteids  are  also 
called  dead  proteids  in  distinction  from  the  living  proteids 
of  the  tissues. 

The  term  "  living  proteids  "  originated  from  the  idea  that  the 
proteids  of  the  living  substance,  because  of  its  peculiar  reactions, 
have  different  chemical  properties  and  constitution  from  the 
unorganized  proteids.  That  such  a  difference  exists  cannot  be 
doubted,  but  what  the  difference  is,  is  not  known. 

Recently  peculiar  phenomena  have  been  observed  in  the  plasma 
which  have  been  ascribed  to  the  action  of  the  proteids  of  the 
plasma.  These  phenomena,  the  immuning  and  bactericidal  action 
of  serum  proteids  upon  pathogenetic  micro-organisms,  cannot  be 
explained  bv  the  physical  and  chemical  properties  of  dead  proteids 
and  are  therefore  regarded  as  vital  phenomena. 

II.    Combined  proteids  are  compounds  of  simple   proteids 

with    other    complex    substances.      They   give    the    general 

proteid  reactions.      They  are  precipitated  by  alcohol  and,  if 

the  action   is  continued  for  a   long  time,  are   coagulated   by 

it.      ldie\-  arc   precipitated   by  making  the   solutions  weakiy 

acid,  but  are  readily  soluble  in  weak  alkalies. 

Although  the  substances  included  in  this  group  differ  greatly 
from  each  other,  still  they  have  this  in  common,  that  they  are 
present  in  the  tissue  cells  as  organized  proteids,  or  at  least  origi- 
nate from  decomposing  protoplasm. 

In  this  class  belong: 

(i)   Compounds  of  simple  proteids  and  pigments. 

Haemoglobin,  the  important  constituent  of  the  red-blood 
corpuscle,  is  composed  of  globin,  a  proteid,  and  haematin, 
an  organic  pigment  containing  iron.  No  successful  analysis 
of  human  haemoglobin  has  been  made.  Haemoglobin  of  the 
dog  has   the  following  composition:   C    54-57$;    H    7.22^; 


CHEMICAL    COMPOSITION   OF    THE   HUMAN  BODY  Z2> 

N  16.38$;  O  20.93^';  S  0.568^;  Fe  0.336^.  If  haemo- 
globin contained  one  atom  of  iron,  the  empirical  formula 
would  be  C636H1025N164O181S3Fe. 

Haemoglobin  is  soluble  in  water  and  crystallizes  directly 
from  its  aqueous  solutions  in  red,  double-refractive  prisms 
and  needles.  Haemoglobin  solutions  absorb  the  yellowish- 
green  light  of  the  solar  spectrum.  This  is  characteristic  of 
haemoglobin  and  may  serve  for  the  detection  of  blood  pig- 
ment. 

Haemoglobin  is  decomposed  and  coagulated  by  heating. 
It  gives  most  of  the  proteid  reactions.  By  boiling  with 
alkalies  and  lead  acetate,  however,  it  does  not  yield  lead 
sulphide. 

Haemoglobin  forms  more  or  less  unstable  compounds  with 
oxygen,  carbonic  oxide,  and  nitric  oxide.  The  compound 
with  oxygen  is  called  oxyhemoglobin  and  is  of  great  physio- 
logical importance. 

Oxyhemoglobin  contains  one  molecule  of  haemoglobin  and 
one  of  oxygen  or  two  atoms  of  oxygen  to  each  atom  of  iron. 
The  oxygen  is  held  but  feebly,  for  even  at  body  temperature 
the  oxyhaemoglobin  decomposes  into  haemoglobin  (also 
called  reduced  haemoglobin)  and  free  oxygen.  Oxyhaemo- 
globin is  also  reduced  by  putrefying  substances  and  by 
ammonium  sulphide. 

Oxyhaemoglobin  has  two  absorption  bands  in  the  yellow- 
green  of  the  spectrum  between  the  D  and  E  lines.  Reduced 
haemoglobin  has  but  one  broad  band  in  the  yellow-green. 

j\Iethce?noglobm  is  a  stronger  union  of  haemoglobin  with  oxygen. 
It  is  formed  by  the  addition  of  potassium  ferricyanide  to  oxyhemo- 
globin; it  is  reduced  by  ammonium  sulphide.  It  has  four 
absorption  bands,  one  of  which,  situated  in  the  red,  is  very 
characteristic. 

The  compounds  of  haemoglobin  with  carbon  monoxide  and 
nitric  oxide  are  of  interest  only  as  they  are  frequently  the  cause 
of  death.  This  is  especially  true  of  CO-hcemoglobin.  Carbonic 
oxide  forms  a  stronger  union  with  haemoglobin  than  oxygen  does; 
it  therefore  drives  out  from  the  oxyhaemoglobin  the  oxygen  which 
is  absolutely  necessary  for  life.  A  solution  of  CO-hsemoglobin 
has  a  cherry-red  color  and  a  spectrum  similar  to  ihat  of  oxyhaemo- 


34  HUMAN  PHYSIOLOGY 

globin,  but  ammonium  sulphide  does'  not  change  its  two  absorp- 
tion bands  to  the  single  absorption  band  of  reduced  haemoglobin. 
CO -haemoglobin  gives  a  bright-red  precipitate  with  sodium  hydrate 
or  with  potassium  ferrocyanide  and  acetic  acid. 

By  acids  and  alkalies,  haemoglobin  is  broken  up  into  its 
components,  globin  (96$)  and  haematin  (4$). 

Globin  is  a  globulin-like  proteid,  showing  all  the  charac- 
teristics of  a  proteid,  but  containing  no  sulphur  which  is 
easily  split  off. 

Hcematin,  C32H32N404Fe,  is  insoluble  in  water,  but  soluble 
in  dilute  acids  and  alkalies  and  in  alcohol  containing  am- 
monia or  sulphuric  acid.  The  brownish-red  acid  haematin 
solution  has  four  absorption  bands  (like  the  methaemo- 
globins) ;  the  carmin-red  alkaline  solution  has  but  one  absorp- 
tion band,  located  in  the  orange.  '  By  ammonium  sulphide, 
haematin  is  reduced  to  haemochromogen,  which  has  two 
absorption  bands  in  the  green.  Haematin  therefore  corre- 
sponds to  oxyhaemoglobin ;  haemochromogen,  to  reduced 
haemoglobin. 

If  haematin  is  boiled  with  a  little  NaCl  and  acetic  acid  and  the 
mixture  is  allowed  to  cool  and  evaporate,  brown  crystals,  the 
so-called  TeichmanrCs  hcemin  crystals,  are  produced.  Hsemin  is 
haematin  hydrochloride.  This  reaction  can  be  used  in  the  detec- 
tion of  blood.  The  reaction  succeeds  still  better  if  potassium 
iodide  is  used  instead  of  NaCl;  in  this  case  the  crystals  are 
haematin  hydroiodide. 

Bv  the  action  of  strong  sulphuric  acid,  haematin  loses  its  iron 
and  hsematoporphyrin  is  formed.  This  is  a  red  pigment  and  has 
a  narrow  absorption  band  in  the  orange  and  a  broad  band  in  the 
yellow-green.  For  the  physiological  importance  of  haemoglobin, 
see  Chapters  II  and  III. 

Hcematoidin  is  an  orange-colored  pigment  crystallizing  in  rhombic 
tables.  It  is  formed  from  the  blood  pigment  of  old  extravascular 
blood-clots.  It  is  supposed  to  be  identical  with  the  bile  pigment, 
bilirubin. 

Mtianine,  a  black  pigment  found  in  the  body,  is  also  supposed 
to  be  derived  from  the  haemoglobin. 

(2)   Compounds  of  simple  proteids  and  carbohydrates. 
Glyco-proteids .      In  this  class  are  the  mucins  and  mucous 
substances,  found  in  the  secretions  of  the  mucous  glands  and 


CHEMICAL    COMPOSITION   OF    THE  HUMAN  BODY  35 

epithelial  cells  of  mucous  membranes,  and  in  tendons  and 
the  umbilical  cord.  They  are  insoluble  in  water,  but,  because 
of  their  acid  properties,  give  a  neutral,  stringy  solution  with 
weak  alkalies.  They  are  not  coagulated  by  boiling  and  are 
completely  precipitated  from  salt-free  solutions  by  acids  as 
well  as  by  alcohol  and  most  of  the  proteid  precipitants  (not 
by  nitric  acid,  nor  by  acetic  acid  and  potassium  ferro- 
cyanide).  They  give  all  the  color  reactions  of  proteids. 
By  boiling  with  acids,  they  split  up  into  proteid  and  a  poly- 
saccharide, the  animal  gum.  They  serve  to  lubricate  the 
mucous  membranes,  and  to  shield  them  from  mechanical  and 
chemical  injuries. 

(3)  Compounds  of  proteid  with  substances  containing 
phosphorus  are  nucleins  and  nucleo-albumins. 

(a)  Nucleins,  so  called  because  they  were  first  obtained 
from  the  nuclei  offish-blood  corpuscles,  are  divided  into: 

{a)  Paranucleins,  i.e.  compounds  of  proteids  and 
phosphoric  acid. 

(fj)  The  true  nucleins,  i.e.  compounds  of  proteids 
and  nucleic  acids  which  are  composed  of  phosphoric 
acid  and  xanthin  or  nuclein  bases. 

{b)  Nucleo-albumins  or  nucleo-proteids  are  compounds  of 
nuclein  and  proteids.  They  are  found  in  cells  as  the  con- 
stituents of  the  nucleus  and  of  the  protoplasm.  The  chro- 
matin of  the  nucleus  and  probably  the  structure  of  the 
protoplasm  capable  of  staining,  are  composed  of  nucleo- 
proteids.  They  are  insoluble  in  water  but  soluble  in  dilute 
alkalies,  with  which  they  form  neutral  compounds  because 
of  their  strong  acidity.  They  are  precipitated  by  acids  and, 
in  their  precipitated  condition,  they  are  coagulated  by  heat. 
They  also  give  most  of  the  proteid  reactions.  Because  of 
their  readiness  to  break  up,  it  is  difficult  to  isolate  them. 

By  boiling  with  dilute  acids  or  alkalies  the  nuclein  is  split 
from  the  nucleo-albumin  and,  by  continued  action  of  these 
reagents,  this  breaks  up  into  proteid,  phosphoric  acid,  and, 
eventually,  the  xanthin  bases  (xanthin,  guanin,  adenin, 
hypoxanthin,  etc.),  which  are  closely  related  to  uric  acid. 


36  HUM  Ah!  PHYSIOLOGY 

Some  nucleo-proteids  also  contain  iron,  e.g.  the  hcemafogen  of 
the  egg-yolk,  so  called  because  hxmoglobin  is  supposed  to  origi- 
nate from  it. 

The  best-known  nucleo-proteid  is  caseinogen  of  milk. 
It  is  formed  during  secretion  by  the  milk-gland.  It  is  in- 
soluble in  water,  forms  soluble  compounds  with  alkalies  and 
alkaline  earths,  and  is  split  up  by  acids,  yielding  paranuclein. 
Caseinogen  is  not  coagulated  by  boiling,  but  it  is  precipi- 
tated by  weak  acids.  By  the  action  of  the  ferment  rennin 
it  yields  casein,  a  proteid  which  forms  an  insoluble  compound 
with  calcium. 

III.  Proteoses. — The  proteoses  are  the  products  of  the 
splitting  up  of  the  simple  and  combined  proteids.  They  are 
formed  during  digestion  of  proteids  or  by  the  action  of  dilute 
acids  upon  proteids,  and  they  differ  but  little  in  elementary 
composition  from  each  other  and  from  the  proteids  out  of 
which  they  are  formed.  Their  formation  does  not  depend 
upon  deep-seated  chemical  changes  of  the  proteids,  but  only 
upon  the  splitting  up  of  a  large  molecule  into  many  similar 
smaller  molecules,  under  the  assumption  of  water.  It  is 
only  in  the  amount  of  sulphur  they  contain  that  they  differ 
from  each  other  and  from  the  mother-substances. 

In  the  splitting  up  of  simple  proteids  many  intermediate 
products  are  formed  which  are  called  the  albumoses,  while 
the  end-products  are  called  peptones.  According  to  their 
origin,  the  albumoses  are  called  fibrinoses,  globuloses,  vitel- 
loses,  caseoses,  and  myosinoses. 

The  proteoses  (albumoses  and  peptones)  are  all  readily 
soluble  in  water,  except  heteroalbumose,  and  many  of  them 
(peptones  and  some  albumoses)  are  dialyzable.  They  are 
not  coagulated  by  heat;  alcohol  precipitates  them  with 
difficulty  but  does  not  coagulate  them.  They  are  all  levo- 
rotatory.  The  rotatory  power  of  all  the  proteoses  formed 
by  gastric  digestion  from  a  simple  proteid  body  is  greater 
than  that  of  the  undigested  proteid,  but  the  rotatory  power 
of  the  products  formed  by  pancreatic  digestion  is  smaller 
than  that  of  the  original  proteid. 


CHEMICAL    COMPOSITION   OF   THE  HUMAN  BODY  37 

The  proteoses  give  all  the  proteid  color  reactions,  but  not  all 
the  precipitation  reactions. 

The  proteoses  behave  towards  the  mineral  acids  and  bases 
like  amido  acids ;  the  acids  are  simply  added  to  the  ammonia 
group,  and  the  metals  of  the  bases  replace  the  hydrogen  of 
the  carboxyl  groups. 

Proteoses,  like  native  proteids,  are  neutral  because  the  acid 
carboxyl  and  the  basic  ammonium  nucleus  are  both  neutralized  by 
their  intimate  union.  Mineral  acids  destroy  this  union,  the  strong 
acid  replacing  the  carboxyl,  hence  the  compound  formed  is  acid 
because  of  the  free  carboxyl  groups.  If  proteoses  combine  with 
alkali,  the  ammonium  group  is  set  free  and  the  compound  formed 
has  an  alkaline  reaction.  The  power  of  proteoses  to  combine 
with  acids  and  alkalies  is  the  greater  the  further  the  splitting  up 
of  the  proteid  has  been  carried;  it  is  greatest  in  peptone  in  which 
the  combining  power  is  many  times  that  of  the  native  proteid. 

The  albumoses  differ  from  the  peptones  not  only  in  the 
size  of  the  molecule  and  the  percentage  of  suphur,  but  also 
in  the  precipitation  by  salts.  Atbumoses  are  precipitated  by 
saturating  their  solution  with  ammonium  sulphate ;  peptones 
are  not  thus  precipitated. 

Albumoses  are  divided  into  primary  and  secondary  albu- 
moses which  differ  from  each  other  in  their  solubility.  The 
primary  albumoses  (protalbumose  and  heteroalbumose)  are 
precipitated  from  a  neutral  solution  by  saturating  with  XaCl. 
The  secondary  albumoses  (deuteroalbumose)  are  thus  pre- 
cipitated only  from  acid  solutions ;  sometimes  they  are  not 
precipitated  by  NaCl  at  all. 

The  secondary  albumoses  are  with  greater  difficulty  precipitated 
by  other  reagents  also;  they  are  not  precipitated  by  nitric  acid  or 
2$  copper  sulphate  solutions,  and  their  precipitation  by  potassium 
ferrocyanide  and  acetic  acid  is  slow  and  incomplete.  The  primary 
albumoses  obtained  from  the  crystallized  serum  albumin  contain 
more  firmly  combined  sulphur,  the  secondary  has  more  loosely 
combined  sulphur. 

Judging  from  the  freezing-point,  it  is  supposed  that  deutero- 
albumose has  a  larger  molecular  weight  than  protalbumose. 
Hence  the  deuteroalbumoses  cannot  be  regarded  as  the  splitting- 
up  products  of  protalbumoses. 

Peptones  are  not  precipitated  by  any  proteid  precipitant 


38  HUMAN  PHYSIOLOGY 

except  tannic  and  phosphotungstic  acid.  They  are  more 
dialyzable  than  the  albumoses,  yet  their  power  of  dialyzing 
is  only  one-fourth  of  that  of  grape-sugar.  They  are  solu- 
ble in  all  proportions  in  water.  Their  solutions  have  a  dis- 
agreeable bitter  taste. 

The  red  color  which  peptones  give  in  the  biuret  reaction 
is  highly  characteristic  of  peptones,  the  other  proteids  giving 
a  reddish-violet  color. 

The  various  peptones  differ  from  each  other  in  the  amount 
of  sulphur;  some  have  loosely  combined  sulphur,  others  have 
only  firmly  combined  sulphur.  They  also  differ  in  their 
behavior  towards  the  pancreatic  ferment  trypsin  ;  the  "  hemi- 
peptones  ' '  are  split  by  trypsin  into  leucine,  tyrosine,  and 
aspartic  acid,  etc.  ;   the  "  anti-peptones  "  not. 

Nothing  is  definitely  known  as  to  the  number  of  peptone  mole- 
cules formed  from  one  molecule  of  simple  proteid.  From  a 
molecule  of  crystallized  serum  albumin,  if  the  calculated  molecular 
weight,  17,070,  is  correct,  at  most  ten  molecules  of  peptones  can 
be  formed,  for  one  molecule  of  serum  albumin  contains  ten  atoms 
<>f  sulphur  and  each  molecule  of  peptone  must  contain  at  least  one 
atom  of  sulphur,  since  peptone  must  still  be  regarded  as  a  proteid. 

Albumoses  and  peptones  are  found  only  in  the  alimentary 
canal,  having  been  produced  by  the  digestion  of  the  proteids 
of  the  food.  By  their  formation,  the  insoluble  and  coagu- 
lable  or  at  least  undialyzable  proteid  of  the  food  is  rendered 
into  a  soluble  and  dialyzable  form  suitable  for  absorption. 

Proteoses-like  bodies  are  also  formed  from  native  proteids  by 
the  action  of  superheated  steam.  The  products  thus  formed  are 
called  atmidalbumoses  and  atmidpeptones.  They  have  no  loosely 
combined  sulphur  and  differ  from  the  ordinary  proteoses  in  their 
precipitation.  Atmidproteoses  are  not  readily  absorbed  from  the 
intestine.  Evidently  by  superheated  steam  the  proteids  are  not 
only  split  up  but  undergo  other  changes  which  make  them  more 
or  less  unsuitable  for  nutrition. 

IV.  Albuminoids  are  derivatives  of  proteids,  which  still 
have  the  characteristic  percentage  composition  of  proteids, 
but  differ  from  them  chemically,  physically,  and  especially 
physiologically.  Some  of  the  albuminoids  contain  more 
sulphur,  others   less,  than  the  proteids.      They  do   not  give 


CHEMICAL    COMPOSITION   OF   THE  HUMAN  BODY  39 

all  the  characteristic  color  reactions,  because  some  do  not 
have  the  aromatic  groups,  hence  all  of  them  do  not  yield 
tyrosin  when  boiled  with  alkalies.  They  do  not  dissolve 
but  swell  up  in  water.      They  are  not  coagulated  by  heat. 

Physiologically  they  differ  from  the  proteids  in  that  they 
are  either  indigestible,  or,  if  they  can  be  digested  and 
absorbed,  they  cannot  replace  the  used-up  body  proteids  as 
the  other  proteids  can. 

Also  in  regard  to  their  functions  in  building  up  the  body, 
there  is  a  great  difference  between  the  albuminoids  and  the 
simple  and  combined  proteids.  The  latter  form  the  bases 
of  the  living  substance,  and  as  such  are  the  chief  constituents 
of  the  cells.  The  albuminoids,  on  the  contrary,  are  present 
only  as  intracellular  substances ;  they  are  indeed  cell- 
products  and  perhaps  take  a  part  in  cellular  metabolism,  but 
their  chief  physiological  importance  lies  in  their  furnishing 
the  material  for  covering  and  framework.  They  form  the 
organic  ground-substance  of  bones,  cartilage,  tendons,  fasciae, 
connective  tissue  and  of  the  covering  of  the  body — epidermis, 
hair  and  nails.  They  are  the  most  important  organic  con- 
stituents which  furnish  form  and  stability  to  the  bod}'. 

The  albuminoids  are  specific  animal  products.  They  are 
formed  by  the  cells  themselves,  being  the  intracellular  sub- 
stance. In  the  epidermal  cells  all  the  protoplasm  is  changed 
to  a  certain  kind  of  albuminoid  substance.  They  are  formed 
from  the  proteids  of  the  cells  by  chemical  changes  the 
nature  of  which  is  still  unknown. 

Albuminoids  unite  with  acids  and  alkalies ;  in  some  of 
them  the  amido-acid  character  is  even  more  apparent  than 
in  the  other  proteids.  By  digestion,  albuminoids,  if  at  all 
digestible,  yield  proteoses-like  products. 

Among  the  albuminoids  are : 

1.  Keratin,  the  chief  constituent  of  the  horny  epithelial  cells, 
hair,  nails,  and  of  the  membrane  of  nerves  (here  called  neuro- 
keratin). It  is  rich  in  sulphur  (2-5$),  most  of  which  is  loosely 
combined  so  that  it  is  easily  split  off  by  alkali.  It  gives  all  the 
proteid  reactions  and  in  decomposing  yields  tyrosin.      It  is  not 


40  HUM  AM    PHYSIOLOGY 

soluble   in   water;  in   general,  it  is  not   soluble  without   previous 
decomposition.      It  cannot  be  digested. 

2.  Elastin,  from  the  elastic  fibres,  has  only  firmly  combined 
sulphur.  It  gives  the  color  reactions  of  proteids  and  yields  the 
corresponding  decomposition  products.  It  is  insoluble  in  water 
and  can  be  digested  by  pancreatic  juice,  not  by  gastric  juice. 

3.  Collagen  forms  the  greater  part  of  the  albuminoids 
found  in  our  body.  It  forms  the  fibres  of  the  connective 
tissue  and  the  organic  basis  of  bones  and  cartilages.  It 
contains  no  loosely  combined  sulphur,  does  not  give  Adam- 
kiewicz's  and  Millon's  reactions,  neither  does  it  yield  tyrosin 
when  decomposing,  hence  it  contains  no  aromatic  group. 
It  contains  a  little  more  oxygen  than  the  proteids,  hence  it 
is  perhaps  formed  from  proteids  by  oxidation. 

If  collagen  is  boiled  for  a  long  time  in  water,  it  takes  up 
water  and,  on  cooling,  a  solid  jelly  called  gelatin  is  formed. 
If  gelatin  is  heated  to  1300  it  again  changes  to  collagen. 
Gelatin  is  the  hydrate  of  collagen.  It  is  soluble  in  hot  but 
not  in  cold  water  (the  reverse  of  native  proteids) ;  in  cold 
water  it  only  swells  up. 

Gelatin  is  not  precipitated  by  mineral  acids,  by  potassium 
ferrocyanide  and  acetic  acid,  nor  by  salts  of  heavy  metals 
(except  mercuric  chloride  in  hydrochloric  acid).  It  is, 
however,  precipitated  by  salts.  It  gives  the  biuret  and 
xanthoproteic  test. 

Gelatin  is  digested  with  difficulty  by  pepsin  but  readily  by 
trypsin,  gelatoses  and  gelatin  peptones  being  formed. 
Concerning  the  importance  of  gelatin  as  a  food  see  Chapter 
VIII. 

4.  Chondrin  is  a  mixture  of  gelatin  and  chondroitin-sulphuric 
acid  which  is  an  ethereal  sulphate  of  chondroitin,  a  nitrogenous 
derivative  of  carbohydrates;  it  can  be  isolated  from  cartilage  by 
dilute  alkalies.  If  bones  are  boiled  with  dilute  mineral  acids,  the 
chondroitin  yields  acetic  acid  and  the  nitrogenous  chondrosin. 
Chondrosin  reduces  cupric  oxide  in  alkali  solutions,  and  by  boil- 
ing with  barium  hydrate  yields  glycuronic  acid  and  glucosamine. 

Ferments.  —  Among  the  proteid-like  bodies  arc  also 
counted   the   unformed    ferments.      The    composition   of  the 


CHEMICAL    COMPOSITION   OF    THE   HUMAN  BODY  4r 

ferments  is  unknown,  but  they  have  some  properties  in 
common  with  proteids.  They  are  soluble  in  water  and 
glycerin,  are  precipitated  and  partly  coagulated  by  alcohol, 
can  be  precipitated  by  salts,  are  not  dialyzable,  and  give  the 
proteid  color  reactions.  They  are  products  of  cellular 
activity. 

The  unformed  ferments  here  referred  to  are  to  be  distinguished 
from  the  formed  ferments  which  are  organisms  (bacteria,  fungi,) 
which,  by  contact,  split  up  certain  substances  (e.g.  yeast,  bac- 
terium lactis.     See  page  20). 

Their  most  important  property  is  that,  in  very  small  quan- 
tities, they  can  chemically  change  unlimited  quantities  of 
certain  substances,  without  suffering  any  chemical  change 
themselves.  Their  action,  in  general,  consists  in  a  hydro- 
lytic  splitting  up  of  the  large  molecule  into  smaller  mole- 
cules and  in  transforming  the  chemical  potential  energy  into 
kinetic  energy.  Their  action  depends  upon  the  reaction  and 
concentration  of  the  solution  of  the  substances  upon  which 
they  act.  The  more  concentrated  the  solutions,  the  less 
active  are  the  ferments.  They  are  rendered  inactive  by 
heating. 

Ferments  are  classified  as : 

1.  Coagulative  ferments,  which  split  up  certain  soluble  proteids 
into  an  insoluble  and  soluble  part  (e.g.  the  coagulative  ferment 
of  blood,  rennin  of  the  stomach,  myosin  ferment). 

2.  Digestive  ferments,  which,  by  hydrolylic  splitting  up,  change 
the  insoluble  or  soluble  proteid  of  food  not  capable  of  absorption 
into  a  soluble  form  capable  of  absorption.      These  include: 

(a)  Diastatic  ferment  (in  saliva  and  pancreatic  juice),  which 
changes  starch  to  sugar. 

(b)  Proteolytic  ferment  (in  gastric  and  pancreatic  juices),  which 
changes  simple  proteids  to  proteoses. 

(c)  Stereolytic  ferment  (in  pancreatic  juice)  which  split  neutral 
fats  into  fatty  acids  and  glycerin. 

Concerning  the  action  of  these  ferments  in  detail,  consult  the 
proper  section  in  special  physiology. 


42  HUMAN  PHYSIOLOGY 


3.   END-PRODUCTS    OF    METABOLISM 

To  this  class  belong  the  substances  which  arc  formed  by 
the  combustion  of  the  energy-yielding  substances  of  the 
body  (proteids,  fats,  carbohydrates).  These  products  are 
excreted  from  the  body. 

It  is  possible  and  even  probable  that  the  end-products  of  meta- 
bolism are  not  formed  directly  by  combustion  from  the  body- 
substance,  but  that  a  series  of  intermediate  substances  are  formed. 
But  nothing  is  known  concerning  these  intermediate  products; 
everything  that  has  hitherto  been  said  about  them  is  based  on 
mere  assumption.  We  must  therefore  be  satisfied  with  enumerat- 
ing the  end-products. 

Among  the  end-products  we  may,  in  the  first  place,  name 
the  already  mentioned  water  and  carbon  dioxide,  the  chief 
combustion  products  of  all  organic  substances. 

In  abnormal  conditions,  organic  substances  of  carbon,  hydrogen 
and  oxygen  which  can  still  undergo  oxidation  are  excreted  from 
the  body.  These  are,  evidently,  products  of  incomplete  combus- 
tion.     Such  substances  are: 

i.    Lactic  acid,  C..H(.0,.      There  are  three  lactic  acids. 

(a)  Ethyline  lactic  acid,    CH.,OH.CH„.COOH,  is  present 
in  the  body  in  but  very  small  quantities. 

(b)  Ethyliden  lactic' acid,  CH3.CHOH.COOH.      Of  these 
there  are  two : 

(i)  The  optically  inactive  fermentation  lactic  acid, 
formed  by  the  lactic-acid  fermentation  of  carbo- 
hydrates. 

(2)   Dextrorotatory  sarcolactic  acid,   found    in    the 
muscles  and  in  urine. 
Sarcolactic  acid   is  a  syrupy  fluid,  soluble  in  water,  alcohol  and 
ether.      It  forms  a  characteristic  crystallizable  salt  with  zinc;  this 
is  of  use  in  isolating  tin-  sarcolatic  acid. 

Lactic  acid  is  present  in  the  urine  if  the  supply  of  oxygen  is 
deficient  (dyspnoea). 

2.  /?-oxybutyric  acid,  CHrCHOII.CH.,.COOH,  diacetic  acid, 
CH3.CO.CH2.COOH,  and  acetone,  CH8.CO.CHs,  appear  in  the 
urine  in  certain  diseases,  especially  diabetes.  Acetone  is  present 
in  normal  urine  in  very  small  quantities. 

3.  It  may  here  be  mentioned  that  oxalic  acid,  COOH.COOH, 


CHEMICAL    COMPOSITION   OF    THE  HUMAN  BODY  43 

is  present  in  small  quantities  in  the  urine  (in  the  form  of  calcium 
oxalate,  yielding  the  "envelope  crystals"'). 

While  the  combustion  of  fats  and  carbohydrates  yields 
only  CO.,  and  H.,0,  combustion  of  proteids  furnishes  these 
and  a  series  of  other  products  which  contain  the  nitrogen, 
sulphur,  and  phosphorus  of  the  proteid.  These  products  are 
of  importance  in  estimating  the  extent  of  proteid  metabolism. 

By  the  combustion  of  the  proteid,  its  sulphur  and  phos- 
phorus form  sulphuric  and  phosphoric  acids,  which  are 
excreted  in  the  form  of  salts. 

The  nitrogenous  cud-products  of  metabolism  can  unite 
with  still  more  oxygen;  hence,  in  the  physiological  combus- 
tion of  proteids,  the  proteids  are  not  fully  oxidized,  but  an 
oxidizable  residue  is  left  which  cannot  be  used  in  the  bodv. 
The  nitrogeneous  end-products  are: 

1 .  Ammonia,  excreted  in  small  quantities  as  ammonia 
salts. 

2.  Urea,  CO(NH2)„ ,  the  diamid  of  carbonic  acid  or 
carbamid. 

Urea  crystallizes  in  colorless  needles  or  long,  rhombic 
prisms  ;  it  is  neutral  and  has  a  cool  saltpetre  taste.  It  melts 
at  130-132°  C,  but  in  solutions  undergoes  decomposition 
at  60-700  C.  It  is  soluble  in  water  and  in  alcohol,  but  not 
in  ether. 

Decomposition  of  urea. — On  heating,  dry  urea  forms  am- 
monia and  biuret.  Two  molecules  of  urea  form  one  mole- 
cule of  biuret  and  one  of  ammonia. 

2CO(NH2)2  =  NH2.CO.NH.CO.NH2+  NH;r 

Biuret  gives  a  reddish-violet  color  with  copper  sulphate 
and  potassium  hydrate  (origin  of  the  term  biuret  reaction). 

By  heating  with  baryta- water,  alkalies,  and  by  the  action 
of  certain  micro-organisms  (during  alkaline  urine  fermenta- 
tion) urea  takes  up  water  and  forms  ammonium  carbonate. 

An  alkaline  solution  of  sodium  hypobromite  decomposes 
urea  into  carbon  dioxide,  water  and  nitrogen: 

CO(NH2)2  +  3XaOBr  =  sNaBr  -f  C02  -f  2H20  -f  Nr 


44  HUMAN   PHYSIOLOGY 

Compounds  of  urea. — With  many  acids  and  bases,  urea 
forms  characteristic  compounds.  The  acids  unite  with  the 
ammonia  group,  in  which  the  nitrogen  becomes  quinquiva- 
lent.     The  most  important  compounds  are : 

(a)  Urea  nitrate,  CO(NH2)2.HN03.  It  crystallizes  in 
smooth,  hexagonal,  colorless  platelets,  soluble  in  pure  water 
but  soluble  with  difficulty  in  water  containing  nitric  acid. 
The  crystals  are  obtained  by  adding  an  excess  of  strong 
nitric  acid  to  a  concentrated  solution  of  urea.  The  com- 
pound serves  for  the  detection  and  isolation  of  urea. 

(I?)  Urea  oxalate,   [CO(NH2)J2.C,H,04. 

(c)  A  white  precipitate  is  formed  when  a  urea  solution  is 
mixed  with  a  solution  of  mercuric  nitrate.  The  proportion 
in  which  urea  and  mercuric  nitrate  unite  varies  with  the  con- 
centration of  the  urea  and  the  mercuric  nitrate  used.  Upon 
the  precipitation  of  urea  by  mercuric  nitrate  depends  Liebig's. 
titration  method  for  estimating  urea. 

Synthesis  of  urea. — Urea  is  formed: 

i .    By  heating  ammonium  cyanate  : 

NH4.O.CN  =  CO(NH2)2.      (Wohler,   1828.) 

2.  By  heating  ammonium  carbonate  with  metallic  sodium, 
water  being  split  off. 

3.  By  passing  an  alternating  electrical  current  through  a 
solution  of  ammonium  carbamate,  NH.,.COONH4,  water 
being  split  off  from  the  ammonium  carbamate. 

4.  From  carbonylchloride  and  ammonia: 

COCL,  +  2NH,  =  CO(NH2)2  +  2HCI. 

5.  From  ethyl  carbonate  and  ammonia: 
C03(C2H5)2  +  2NH3  =  2(C,H..OH)  -J-  CO(NH2)2. 

Presence  and  formation  of  urea  in  the  animal  body — Urea 
forms  most  of  the  solids  of  the  urine  of  mammals.  It  is 
present  in  small  quantities  in  the  blood,  in  all  tissue  fluids, 
and  in  many  organs  of  the  body. 

Urea  is  the  most  important    nitrogenous  end-product  of 


CHEMICAL    COMPOSITION   OF   THE  HUMAN  BODY  45 

proteid  combustion.  Other  nitrogenous  end-products  are 
present  in  but  small  quantities.  The  amount  of  urea  ex- 
creted depends,  therefore,  upon  the  extent  of  proteid  meta- 
bolism. 

A  large  portion  of  the  urea  is  formed  in  the  animal  body- 
synthetically  from  the  combustion  products  of  proteids, 
namely,  carbon  dioxide  and  ammonia.  That  this  formation 
is  possible  is  proven  by  the  following  facts : 

Certain  ammonia  salts,  especially  ammonium  carbonate, 
introduced  into  the  body  do  not  appear  in  the  urine  as 
ammonia  salts,  but  the  amount  of  urea  is  increased  in  pro- 
portion to  the  ammonia  salts  taken.  This  is  also  true  for 
some  substituted  ammonia  compounds,  such  as  amido  acids 
(leucine,  glycocoll,  tyrosine  and  others). 

That  the  ingested  ammonia  salt  is  really  changed  to  urea  and 
•does  not  merely  increase  proteid  decomposition  and  thus  the 
excretion  of  urea,  is  proven  by  the  fact  that  if  a  substituted 
ammonia  salt  is  ingested,  the  corresponding  substituted  urea  is 
formed.  If  meta-amido-benzoic  acid,  NH.,.C\H,.COOH,  is  in- 
gested,  we  find  uramidobenzoic  acid,  NH,,C0.NH.C).H4.COOH. 

The  place  where  the  synthetical  formation  of  urea  from 
ammonia  takes  place  is  the  liver.  If  defibrinated  blood  con- 
taining ammonium  carbonate  is  passed  through  an  excised 
liver,  into  the  portal  vein  and  out  of  the  hepatic  vein,  the 
ammonium  carbonate  decreases,  while  the  urea  increases,  in 
the  blood.  If  the  liver  is  artificially  cut  off  from  the  circula- 
tion, the  amount  of  urea  is  decreased,  while  the  amount  of 
ammonia  and  also  of  amido  acids  (leucine,  tyrosine)  in  the 
urine  is  increased.  This  is  also  true  for  many  diseases  of 
the  liver. 

The  nature  of  the  substituted  urea  shows  the  part  played  by  the 
carbamic  acid  in  urea  formation.  Perhaps  carbamic  acid  and 
ammonia  are  formed  by  the  proteid  metabolism  and  that  these 
substances  are  changed  to  urea  in  the  liver.  Hence  urea  must  be 
regarded  as  the  amid  of  carbamic  acid. 

The  object  of  the  formation  of  urea  from  ammonia  salts 


46  Hi' MAS   PHYSIOLOGY 

seems  to  be  to  change  the  injurious  ammonia  formed  by 
proteid  metabolism  into  a  harmless  compound. 

It  is  a  question,  however,  whether  all  the  urea  formed  in 
the  body  is  derived  from  ammonia  or  ammonia  derivatives. 
it  is  probable  that  some  of  the  urea  can  also  be  directly  split 
off  from  the  proteid. 

3.   Uric  acid,  C.r^X/),,  has  the  structural  formula: 

NH-CO 

/  ' 

\  pCO.   [Diureid  of  trioxyacrylic  acid.] 

\XH-C-XH/ 

Pure  uric  acid  crystallizes  in  colorless,  rhombic  prisms,  but 
directly  from  the  urine  it  yields  bundles  of  colored  dumb- 
bell and  whetstone  crystals.  Uric  acid  is  but  slightly  solu- 
ble in  cold  water  (0.05  g  in  one  liter);  it  is  a  little  more 
soluble  in  hot  water  (0.5  g  in  one  liter)  or  in  the  presence 
of  urea ;  it  is  insoluble  in  alcohol  and  ether.  As  a  dibasic 
acid  it  forms  neutral  and  acid  salts.  The  neutral  alkali 
salts  are  quite  soluble  in  water;  the  acid  salts  are  also  more 
soluble  than  the  free  acid.  But  these  are  precipitated  even 
by  the  cooling  of  the  urine  and,  as  they  take  with  them  the 
pigments  of  the  urine,  they  form  reddish  precipitates  (sedi- 
mentum  lateritium). 

The  salts  of  uric  acid  with  the  alkali-earths,  most  of  the 
metals,  and  also  ammonia  are  not  very  soluble  in  water. 

Because  of  the  comparative  insolubility  of  uric  acid,  it  is 
easily  deposited  in  the  kidneys,  ureters  and  the  tissues  of  the 
body  (gravel,  gout). 

If  uric  acid  to  which  nitric  acid  has  been  added  is  evap- 
orated to  dryness  and  to  the  residue  ammonia  is  added,  a 
reddish-violet  color  results  which  gives  place  to  a  bluish 
violet  on  addition  of  sodium  hydrate  {inurexide  test  for  uric 
acid). 

By  careful   oxidation   of   uric   acid,    allantoin   and   carbon 
dioxide    are    formed:     C.H4N40,  -f  O  +  H20  =  C4H6N4Oa 
allantoin;  -f  C02. 


CHEMICAL    COMPOSITION   OF   THE  HUMAN  BODY  47 

Allantoin  is  found  in  the  allantoic  fluid  and  in  the  urine  of 
newly  born  mammals.  On  oxidation  it  yields  urea  and  oxalic 
acid:  C4H6N403  +  O  +  2H./J  =  2CO(NH,)2  +  C204H2. 

Uric  acid  can  be  formed  synthetically: 

(a)  By  melting  urea  and  glycocoll  together: 

3CO(NH2)2  +  NH2.CH2COOH  =  C5H4N403-f3NH3-f2H20. 

(/;)   From  urea  and  trichlorlactamide : 
2CO(NH2)2+C3Cl302H2NH2=C5H4N403+ClNH4+H20+2HCI. 

Presence  and  formation  of  uric  acid  in  the  animal  body. — 
Uric  acid  is  found  in  small  quantities  in  the  urine,  also  in 
the  blood  and  the  organs  of  the  mammals.  It  is  the  chief 
constituent  of  the  urine  of  birds  and  reptiles.  It  is  formed, 
like  urea,  from  the  decomposed  proteids.  In  the  liver  of 
birds,  uric  acid  appears  to  be  formed  synthetically  from 
lactic  acid  and  ammonia  salts.  If  the  liver  of  a  bird  be 
extirpated,  the  urine  contains  lactic  acid  and  ammonia  salts 
instead  of  uric  acid.  Urea  and  amido  acids  given  to  birds 
is  excreted  in  the  form  of  uric  acid.  Whether  in  mammals 
uric  acid  is  also  formed  synthetically  is  not  known. 

Uric  acid  is  closely  related  to  the  nuclein  bases;  by  reduc- 
tion it  can  be  changed  to  xanthin  and  hypoxanthin  (see 
below).  Hence  it  is  formed  in  the  animal  body  probably 
by  the  splitting  up  and  oxidation  of  the  nucleins. 

It  is  supposed  that  the  uric  acid  is  especially  formed  from  the 
nucleins  of  the  nuclei  of  the  decomposed  leucocytes.  This  is 
based  upon  the  facts  that  large  increase  and  greater  destruction 
of  leucocytes  in  the  blood  (leukaemia)  is  accompanied  by  greater 
excretion  of  uric  acid,  and  that  by  heating  the  pulp  of  spleen  or  a 
boiled  aqueous  extract  of  spleen  with  blood,  uric  acid  is  formed. 
In  this,  however,  the  oxidizing  power  of  the  blood  is  necessary. 

The  excretion  of  uric  acid  is  increased  by  food  rich  in 
nucleins.  Uric  acid  introduced  into  the  body  of  a  mammal 
is,  for  the  greater  part,  excreted  as  urea. 

4.   Nuclein  or  xanthin  bases.     These  are: 

(a)   Guanin,  C.H.N.O. 

\b)  Xanthin,  C.H4X402. 


48  HUMAN  PHYSIOLOGY 

(Y)  Adenin,  C.H.N.. 

{d)   Hypoxanthin,  C5H4N40. 

These  substances  are  closely  related  to  each  other. 
Hypoxanthin  is  an  oxidation  product  of  adenin,  xanthin  is 
an  oxidation  product  of  guanin  and  of  hypoxanthin.  They 
are  regarded  as  the  precursors  of  uric  acid  or  urea,  for  by  the 
reduction  of  uric  acid  xanthin  and  hypoxanthin  can  be  pro- 
duced. They  are  formed  by  the  splitting  up  of  nucleins 
(see  page  35). 

They  are  found  in  small  quantities  in  urine,  blood  and  the 
organs,  especially  the  liver  and  spleen.  Their  excretion  is 
increased  during  leukaemia. 

5.  Hippuric  acid  (Benzoylglycocoll), 

C.H..CO.NH.CH.,.COOH, 

is  found  in  the  urine  of  plant-eaters.  It  is  formed  in  the 
kidneys  by  the  synthesis  of  benzoic  acid,  Ci;H5.COOH,  and 
glycocoll,  NH.CH.-COOH. 

6.  Kreatin  and  kreatinin. 

Kreatin,  C4HgN302,  is  methylguanidin-acetic  acid: 

NH  -  C/NH2 

Guanidin  is  imido-urea:   NH  =  C(NH.,)„. 
Kreatinin,  C,H7N30,  is  the  anhydrid  of  kreatin  : 

/NH-CO 
NH  ~  C<  \ 

\N(CH,)-CH:,. 

Kreatin  can  be  synthetically  formed  from  cyanamid  and  methyl- 
glycocoll  (sarcosin)  : 

.XH  /Nil., 

C^        +NH(CH.i).CH.,.COOH  =  NHzC\ 
NNH  xN(CH3).CH.,COOII. 

Kreatin  and  kreatinin  crystallize  in  monoclinic  prisms.  Both 
are  soluble  in  water.  The  reaction  of  kreatin  is  neutral,  that  of 
kreatinin,  alkaline.  By  the  action  of  alkalies  both  form  decom- 
position products,  among  others,  urea. 


CHEMICAL    COMPOSITION   OF    THE   HUMAN  BODY  49 

If  to  an  alkaline  solution  of  kreatinin  a  few  drops  of 
sodium  nitroprusside  are  added,  a  red  color  is  produced 
which  soon  disappears  (Weyl's  kreatinin  test).  This  color 
is  not  brought  back  by  the  addition  of  acetic  acid,  like  that 
of  aceton.  Kreatinin  unites  with  zinc  chloride,  forming 
kreatinin  zinc  chloride,  a  slightly  soluble,  double  salt  which 
readily  crystallizes. 

Kreatin  is  found  in  the  blood  and  in  many  organs, 
especially  in  the  muscles.  It  is  regarded  as  a  precursor  of 
urea.      Kreatinin  is  a  constituent  of  urine. 

It  is  a  question  whether  the  kreatinin  of  urine  is  formed 
from  the  kreatin  of  the  muscles.  The  amount  of  kreatin  in 
the  muscles  is  said  to  be  increased  by  muscle  activity,  not 
so  the  kreatinin  of  the  urine.  On  the  other  hand,  it  has 
been  observed  that  kreatin  fed  to  animals  increases  the 
amount  of  kreatinin  in  the  urine  correspondingly. 

Carnine,  C_HgN403 ,  is  also  a  constituent  of  muscles.  By  oxida- 
tion with  nitric  acid  it  is  changed  to  hypoxanthin. 

Cystin,  a  nitrogenous  body  found  in  urine  during  pathological 
conditions  (increased  putrefaction  in  the  intestine,  diseases  of 
intestine),  is  the  disulphide  of  amido-ethylidene  lactic  acid: 

CH3\      s_        /CH3 

COOH/v^5     /\COOH. 
NH2  NH2 

Cystin  is  of  interest  because  in  it  sulphur  is  excreted  from  the 
body  in  unoxidized  form. 

7.  Bile  acids  are  the  union  of  a  nitrogenous  with  a  non- 
nitrogenous  acid.  The  nitrogenous  part  is  an  amido-acid 
(glycocoll  or  taurin) ;  the  non-nitrogenous  part  is  a  cholalic 
acid  (or  fellic  acid). 

The  bile  acids  are  soluble  in  water  and  alcohol  but  in- 
soluble in  ether.  They  are  precipitated  in  crystalline  form 
from  the  alcoholic  solution  by  ether.  They  give  a  cherry- 
red  color  with  furfurol,  or  cane-sugar,  and  concentrated 
sulphuric  acid  (Pettenkofer's  test).  They  are  monobasic 
acids  which  form  salts  with  alkalies.  These  salts  are  dextro- 
rotatory. 


5<>  HUMAN  PHYSIOLOGY 

In  human  bile  there  are: 

(a)  Glycocholic  acid,  CgH^NO,.,  a  compound  of  glycocoll 
and  cholalic  acid. 

(J?)  Taurocholic  acid,  C.^H (.XSO. ,  a  compound  of  taurin 
and  cholalic  acid. 

Cholalic  acid,  C.MH4llO.,  is  a  monobasic  acid  with  three 
— OH-groups  (trioxy-acids).  It  is  an  unsaturated  compound 
since  it  unites  directly  with  bromine.  Its  constitution  is 
unknown,  as  is  also  its  origin  in  the  body.  Its  high  per- 
centage of  carbon  makes  it  probable  that  it  is  first  formed  by 
synthesis. 

Beside  cholalic  acid,  there  is  present  in  the  human  bile  another 
non-nitrogenous  constituent  of  the  bile  acids — -fellic  acid,  C2SH40O4. 
In  animals  there  are  still  other  non-nitrogenous  constituents  of 
bile  acids,  closely  related  to  cholalic  acid. 

Glycocoll  (amido-acetic  acid),  NH.,CH.7.COOH,  is  a 
decomposition  product  of  proteids.  It  is  especially  present 
among  the  products  of  the  splitting  up  of  gelatin. 

Taurin  (amido-ethylsulphonic  acid),  NH2.C2H4.S02OH 
(the  sulphur  is  directly  united  with  the  carbon,  hence  a 
sulphonic  acid),  may  also  be  regarded  as  a  metabolic  product 
of  proteid. 

The  bile  acids  are  formed  in  the  liver  and  secreted  in  the 
form  of  sodium  salts.  They  are,  in  part,  absorbed  from  the 
intestine,  in  part  they  are  transformed  into  their  anhydrids 
(dyslysins)  by  putrefaction  in  the  intestine.  The  bile  acids 
aid  the  absorption  of  fats  in  the  intestine  (see  Chapter  X). 

8.    Bile  pigments. — The  most  important  are: 

(a)  Bilirubin,  a  reddish-yellow  pigment,  C32H3gN406. 

(b)  Biliverdin,  a  green  pigment,  C32H36N408, 
Riliverdin  is  an  oxidation  » product  of  bilirubin.      The  bile 

pigments  are  weak  acids,  forming  soluble  salts  with  the 
alkalies  and  insoluble  salts  with  calcium  (this  last  is  found 
in  the  gall-stones). 

Bilirubin  is  slightly  soluble  in  alcohol,  readily  in  chloro- 
form, and  crystalli7.es  in  rhombic  tables.     Biliverdin  is  readily 


CHEMICAL    COMPOSITION   OF   THE  HUMAN  BODY  51 

soluble  in  alcohol,  slightly  in  chloroform.  Bilirubin,  by  the 
reduction  of  nascent  hydrogen,  takes  up  water  and  forms 
Jiydrobiliritbiu,  C.,.,H4uNtO.  ,  which  is  identical  with  urobilin 
(a  pigment  of  urine).  Urobilin  cannot  be  changed  back  to 
bilirubin  by  oxidation. 

Gmelin's  test. —  In  a  test-tube  place  some  nitric  acid  con- 
taining nitrous  acid.  Carefully  cover  it  with  an  aqueous 
solution  of  bile  pigment.  At  the  junction  of  the  two  liquids, 
colored  layers  will  be  seen,  which  from  the  top  downward 
are  green,  blue,  violet,  red,  reddish  yellow.  The  pigments 
to  which  the  colors  are  due  are  formed  by  the  oxidation 
of  bilirubin  or  biliverdin ;  they  represent  various  oxidation 
stages  of  the  bile  pigment. 

The  bile  pigments  are  made  in  the  liver  from  the  haematin 
formed  by  the   decomposition  of  the  red   blood   corpuscles. 
This  haematin  loses  its  iron : 
C,,H,.,NAFe  (haematin) -f  2 H,C> - Fe  =  C0.,H,fiN .0,.  (bilirubin ). 

9.  Besides  the  end-products  of  metabolism  above  named,  there 
are  present  in  the  urine  aromatic  substances.  It  is  not  certain 
whether  these  originate  by  metabolism  or  whether  they  are  merely 
products  absorbed  from  the  alimentary  canal.  By  the  proteid 
putrefaction  in  the  intestine,  aromatic  compounds  are  formed 
(phenol,  aromatic  oxyacids,  indol,  skatol)  which,  in  so  far  as  they 
are  not  cast  out  with  the  faeces,  are  absorbed  by  the  body  and  are 
in  part  oxidized  (forming  indoxyl,  skatoxyl)  and  in  part  united 
with  sulphuric  acid  and  excreted  by  the  kidneys  as  such.  For 
further  information,  see  Chapter  VII  and  Chapter  IX. 


CHAPTER    II 
THE    BLOOD 

BLOOD  is  a  red,  opaque,  salty  fluid,  having  a  character- 
istic smell  and  a  specific  gravity  of  1.053-1.066.  It  has  an 
alkaline  reaction,  the  alkalinity  being  equal  to  that  of  a 
0.2-0.4^  sodium  carbonate  solution. 

The  blood  circulates  through  the  entire  animal  body  in  a 
closed  system  of  vessels  which  is  exceedingly  ramified. 
The  most  important  physiological  import  of  blood  is  to  carry 
foodstuffs  to  the  organs  and  to  remove  the  metabolic 
products. 

Blood  is  composed  of  a  clear  yellowish  fluid,  the  plasma, 
in  which  are  suspended  the  solid  constituents,  the  red  and 
white  blood  corpuscles.  Histologically  considered,  blood  is 
a  tissue  with  a  liquid  intercellular  substance. 

Blood  coagulates  within  a  few  minutes  after  leaving  the 
vessels,  i.e.  it  clots  to  a  jelly-like  mass.  The  coagulation 
depends  upon  the  separation  of  a  proteid  from  the  plasma, 
the  fibrin,  which  forms  a  fibrous  mass  inclosing  the  blood 
corpuscles  in  its  meshes.  Gradually  the  clot  shrinks,  thereby 
pressing  out  a  clear,  faintly  yellowish  fluid,  the  blood  serum. 
The  coagulum  with  the  inclosed  corpuscles  is  called  the 
clot.  Plasma  is  composed  of  serum  and  the  fibrin-forming 
proteid.  Serum  is  plasma  without  its  fibrin-forming  proteid. 
Blood  from  which  the  fibrin  has  been  removed  by  whipping 
(e.g.  with  a  rod)  is  called  defibrinated  blood,  and  is  com- 
posed of  serum  and  corpuscles.  In  whipping  blood,  the 
fibrin  clings  to  the  rod. 

The  quantity  of  blood   in   man  is  about  7.5$  of  the   body 


THE  BLOOD  53 

weight,  hence  adult  man  has  about  five  liters  of  blood,  of 
which  about  35^  vol.  is  blood  corpuscles  and  65$  vol. 
plasma. 

1.   THE    BLOOD     CORPUSCLES 

1.  The  red  blood  corpuscles  of  man  are  soft,  elastic, 
biconcave  disks  with  circular  outlines.  They  are  7— 8/x  in 
diameter,  1.6/.1  thick,  have  a  volume  of  72  a3  and  a  surface 
of  128/A  In  thin  layers  they  are  yellowish  green,  in  thicker 
layers  red ;  they  are  heavier  than  the  plasma  and  therefore 
sink  to  the  bottom  when  blood  is  allowed  to  stand. 

Man  and  most  mammals  have  round,  non-nucleated  red  blood 
corpuscles;  birds,  reptiles,  amphibians  and  fishes  have  oval, 
nucleated  red  blood  corpuscles. 

One  cb.mm.  of  human  blood  contains,  in  the  male  about  five, 
in  the  female  about  4.5  million  red  blood  corpuscles;  their  sur- 
faces are  640  and  576  sq.mm.  respectively.  This  immense  surface 
favors  the  taking  up  and  the  giving  off  of  oxygen  in  external  and 
internal  respiration.  The  number  of  blood  corpuscles  is  found  by 
counting  the  number  found  in  an  accurately  measured  quantity  of 
blood  diluted  to  a  given  extent.  The  counting  is  done  with  the 
aid  of  a  microscope  and  a  specially  constructed  slide. 

The  number  of  red  blood  corpuscles  is  greater  the  higher  the 
altitude. 

The  red  blood  corpuscles  contain  65^  water  and  35$ 
solids.      Of  the  solids  the  most  important  is 

The  red  coloring  matter  of  blood,  haemoglobin,  which 
forms  about  87—95$  °f  the  solid  constituents  of  the  blood 
corpuscle  (11—15$  °f  total  blood);  it  is  deposited  in  the 
framework,  the  stroma,  of  the  blood  corpuscles. 

The  haemoglobin  of  the  blood  corpuscle  becomes  dissolved  in 
the  fluid  of  the  blood  by  the  addition  of  water,  ether,  chloroform 
or  bile  to  the  blood;  also  by  decomposition,  by  freezing,  and  by 
thawing  of  the  blood  and  by  the  passing  through  of  strong  electric 
shocks.  Blood,  in  which  the  coloring  is  dissolved  in  the  fluid,  is 
transparent  (laky-blood). 

The  cause  of  this  dissolving  of  haemoglobin  in  the  blood  fluid 
after  the  addition  of  water,  is  the  disturbance  of  the  osmotic  equi- 
librium between  the  corpuscles  and  the  surrounding  fluid.  The 
corpuscles    swell    by    the    imbibing    of    water    and    are    thereby 


54     •  HUM/IN   PHYSIOLOGY 

destroyed.  Haemoglobin  also  leaves  the  blood  corpuscles  when 
thev  are  placed  in  the  serum  of  another  kind  of  animal.  As  such 
serum  has  all  the  physical  properties  which  make  the  existence  of 
the  blood  corpuscle  possible,  the  cause  of  the  passing  out  of  the 
haemoglobin  must  lie  in  the  chemical  difference  of  the  various  kinds 
of  serum.  These  differences  are  due  to  the  proteids.  The  proteid 
of  one  kind  of  serum  acts  upon  the  corpuscle  of  another  animal  as 
a  poison  (globulicidal  action  of  the  serum). 

The  quantity  of  haemoglobin  is  estimated  by  colorimetry.  A 
measured  quantity  of  blood  is  diluted  with  water  till  it  has  the 
same  color  as  a  haemoglobin  solution  of  known  strength;  from  the 
extent  of  the  diluting,  the  quantity  of  haemoglobin  can  be  found. 

For  the  chemical  properties  of  haemoglobin,  see  page  32. 

Haemoglobin  is  of  physiological  importance  because  of  its 
power  to  unite  with  oxygen,  forming  a  weak  compound 
called  oxyhemoglobin ;  it  therefore  serves  as  the  oxygen 
carrier  (see  pages  33  and  58). 

The  stroma  of  the  red  blood  corpuscles,  which  remains 
behind  after  the  withdrawal  of  the  coloring  matter,  is  com- 
posed of  proteids,  fat,  lecithin,  and  cholesterin.  Besides  these 
substances,  the  red  blood  corpuscles  contain  salts,  especially 
potassium  chloride  and  potassium  phosphate. 

The  red  blood  corpuscles  are  continually  destroyed  in  the 
body  in  large  numbers.  The  places  of  destruction  are  the 
liver  and  the  spleen.  A  restitution  of  this  loss  by  the  forma- 
tion of  new  corpuscles  takes  place  in  the  red  bone  marrow 
(in  the  embryo  also  in  the  liver  and  spleen),  the  corpuscles 
being  formed  from  colored  nucleated  blood  cells,  the 
haematoblasts.  They  are  formed  from  these  haematoblasts 
by  indirect  division.  At  first,  they  still  contain  a  nucleus, 
but  later  on  the  nucleus  disappears. 

2.  The  white  blood  corpuscles,  also  called  leucocytes  or 
lymph  corpuscles,  are  generally  a  little  larger  than  the  red 
corpuscles;  they  are  colorless  cells  with  one  or  more  nuclei. 
They  have  no  constant  shape  as  they  can  change  their  form, 
like  the  amoeba,  and  can  also  move  about  by  the  pushing 
out  and  withdrawing  of  protoplasmic  processes.  At  rest 
they  are  spherical. 


THE  BLOOD  55 

There  are  many  kinds  of  leucocytes,  which  differ  in  their  size 
and  in  the  proportion  of  their  protoplasm  and  nucleus: 

i.  Small  cells  of  4-7/-/  diameter  with  little  protoplasm  and  one 
nucleus;  few  in  number. 

2.  Larger  cells  of  j—ioju  diameter  with  much  protoplasm  and 
one  or  more  nuclei  (large  uni-nuclear  and  poly-nuclear  cells); 
these  make  up  the  bulk  of  the  leucocytes. 

3.  Granular  cells  of  8—14 /^  diameter,  with  many  granules  in 
their  protoplasm;  these  granules  stain  differently  in  different  cells. 
Accordingly,  we  speak  of  oxyphile  (eosinophile),  basophile  and 
neutrophile  cells,  as  the  granules  stain  with  acid,  basic  or  neutral 
stains. 

The  number  of  leucocytes  is  about  10,000  in  one  cu.  mm. 
(about  500  red  to  one  white),  but  it  varies  greatly.  The 
leucocytes  contain  besides  water  chiefly  proteids  (especially 
nucleins  and  nucleo-albumin)  and  in  smaller  quantities 
lecithin,  cholesterin,  and  salts. 

The  white  blood  corpuscles  are  able  to  pass  through  the 
stomata  of  the  walls  of  the  capillaries  and  thus  wander  into 
the  tissues,  hence  they  are  also  called  wrandering  cells. 
They  are  of  physiological  importance  because  they  serve  as 
transports  for  many  undissolved  substances  (fat,  pigment) 
and  because  they  are  able  to  destroy  and  remove  foreign 
bodies  (e.g.  Bacteria).  They  migrate  in  large  numbers 
from  the  vessels  to  those  places  where  foreign  substances 
causing  inflammation  are  present,  and  there  they  form  the 
pus.  They  are  stimulated  to  activity  by  chemical  action. 
They  originate  in  the  lymph  glands  and  spleen  (see  Chapter 
VI). 

Besides  the  red  and  white  blood  corpuscles,  there  are  still  other 
constituents  in  the  blood  having  a  definite  form,  viz.  : 

Blood  platelets,  colorless,  strongly  refractive  disks  having  a 
diameter  of  \  or  \  that  of  the  red  blood  corpuscles.  They  are 
apparently  the  nuclear  remains  of  destroyed  leucocytes. 

Elementary  granules,  i.e.  fat  granules,  which  are  brought  to  the 
blood  by  the  chyle. 

2.   THE   BLOOD    PLASMA 

Pure  plasma  can  be  obtained  by  letting  uncoagulated  blood 
stand  at  low  temperature  (about  o°  C. ).      By  this,  coagulation  is 


56  HUMAN  PHYSIOLOGY 

prevented  and  the  corpuscles  sink  and  the  clear  supernatant  fluid 
is  the  plasma. 

Plasma   is   a   yellowish,    alkaline   fluid,    having   a   specific 
gravity  of  1.03;   it  contains  9$  solids  which  are: 
1.   Proteids  (7-8$: 

[a)   Scrum  albumin  (3—5$). 

The  albumins  differ  from  each  other  in  their  specific  rotatory 
power,  their  coagulation  temperature,  and,  as  far  as  they  are 
crystallizable  (as  in  serum  of  horse  blood),  in  the  forms  of  their 
crystals. 

(/;)    Scrum  globulin  (3-4$). 

The  quantity  of  albumin  and  globulin  varies  much.  In  general 
the  albumin  predominates  in  the  blood  of  well-fed  animals,  while 
globulin  predominates  in  that  of  fasting  animals. 

(r)  Fibrinogen  (0.1-0.3^^. 

Fibrinogen  is  a  globulin-like  proteid  from  which  fibrin  is 
formed  when  blood  coagulates.  The  amount  of  fibrin  is  but 
small  (0.1-0.3$).  Its  volume,  however,  appears  large  as 
it  is  swollen.  The  fibrin  formation  is  most  likely  brought 
about  by  the  splitting  of  fibrinogen  into  two  parts,  one  part 
being  the  insoluble  fibrin,  the  other  a  soluble  proteid  of 
which  little  is  known. 

The  coagulation  is  brought  about  by  an  unformed  ferment 
— thrombin.  This  ferment  is  not  present  in  blood  in  healthy 
blood  vessels.  It  is  formed,  when  blood  is  shed,  by  the 
breaking  down  of  the  white  blood  corpuscles,  especially  the 
poly-nuclear.      Defibrinated  blood  is  called  blood  scrum. 

As  long  as  blood  is  inclosed  in  blood  vessels  having  sound 
walls,  coagulation  does  not  occur.  The  coagulation  of  blood  is 
prevented  by  cooling,  by  the  addition  of  saturated  salt  solutions, 
e.g.  magnesium  sulphate,  and  by  the  addition  of  salts  of  oxalic, 
hydrofluoric,  and  fatty  acids.  Soluble  calcium  salts  seem  to  aid 
in  the  formation  of  the  coagulative  ferment.  The  power  of 
coagulation  can  also  be  destroyed  by  the  injection  of  proteoses 
and  of  leech  extract. 

Coagulation  is  of  importance  in  that  the  bleeding  from 
vessels  is  stopped  by  the  clotting  of  the  shed  blood,  as  the 


THE  BLOOD  57 

clot  formed  closes  the  opening'  of  the  vessel.  In  bleeders 
the  blood  does  not  coagulate,  hence  fatal  bleeding  is  apt  to 
occur. 

2.  Ether  extracts:  Fats,  cholesterin,  the  ester  of  choles- 
terin  and  fatty  acid,  lecithin  (about  5$). 

3.  Carbohydrates  in  the  form  of  grape-sugar  (0.1-0.2$). 
In  the  body  the  carbohydrates  are  carried  in  the  form  of 
grape-sugar  by  the  blood  from  one  place  to  another. 

4.  End-products  of  metabolism  (urea,  uric  acid,  kreatin, 
xanthin,  lactic  acid  and  others)  in  small  quantities. 

5.  Salts  (0.8$),  chiefly  NaCl  (0.6$)  and  neutral  and  acid 
sodium  carbonate ;  also  acid  calcium  carbonate  and  mag- 
nesium sulphate  in  small  quantities. 

Alexines  and  antitoxins  are  proteid-like  substances  found  in  the 
plasma  or  serum  and  protect  the  body  against  infectious  diseases. 
The  alexines  have  a  bactericidal  action,  i.e.  they  destroy  the 
pathogenic  micro-organisms  or  inhibit  their  action.  The  antitoxins 
render  the  poisonous  metabolic  products  (toxins)  of  the  micro- 
organisms harmless.  The  alexines  are  also  responsible  for  the 
globulicidal  action  of  the  blood  serum  (see  page  54). 


CHAPTER    III 

THE    GASES  OF   THE  BLOOD  AND  THE  CHEMISTRY   OF 
RESPIRATION 

1.   THE    GASES    OF    THE    BLOOD 

For  the  analysis  of  the  gases  of  the  blood,  it  is  placed,  at  body 
temperature,  in  a  vessel  from  which  the  air  has  been  removed  by 
a  mercurial  air-pump.  The  gases  leave  the  blood,  entering  into 
the  vessel;   they  can  then  be  collected  and  analyzed. 

The  gases  of  the  blood  are  oxygen,  carbon  dioxide,  and 
nitrogen.  The  oxygen  is  dissolved  physically  to  only  a  very 
small  extent,  the  greater  part  being  chemically  united  to  the 
haemoglobin,  forming  oxyhemoglobin.  The  -oxygen  must 
be  held  chemically,  as  the  quantity  of  the  oxygen  in  the 
blood  is  not  proportional  to  the  partial  pressure-  of  the 
oxygen  upon  the  blood,  as  would  be  the  case  in  a  physical 
solution. 

Oxyhemoglobin  is  a  compound  easily  undergoing  dis- 
sociation ;   by  its  dissociation  the  oxygen  is  set  free. 

The  degree  of  dissociation  of  a  compound,  by  which  a  gas  is 
set  free,  is  dependent  upon  the  temperature  and  the  pressure  of 
the  gas.  In  a  vacuum  and  at  the  body  temperature,  oxyhemo- 
globin undergoes  complete  dissociation  (not  at  o°) ;  in  other 
respects,  the  amount  of  haemoglobin  chemically  united  with  oxygen 
increases  with  the  partial  pressure  of  the  oxygen,  but  not  propor- 
tionally as  in  the  mere  physical  solution. 

The  carbon  dioxide  of  the  blood  is  also  physically  dis- 
solved  to  but  a   small    extent;    most  of  it   being   chemically 

*  Tn  a  mixture  of  gases  the  partial  pressure  of  one  of  the  gases  is  that  part 
.,l  the  whole  pressure  which  the  gas  exerts  by  itself. 

5S 


THE   GASES    OF   THE  BLOOD  59 

bound  to  the  alkalies  of  the  serum  (chiefly  to  the  sodium 
bicarbonate  and,  in  smaller  quantities,  to  the  acid  calcium 
■carbonate).  As  the  whole  blood  contains  more  carbon 
dioxide  than  the  corresponding  amount  of  plasma,  the  blood 
corpuscles  also  contain  this  gas  in  an  easily  dissociated  form, 
perhaps  united  with  the  haemoglobin  or  the  alkali  phosphate. 

In  a  vacuum,  the  blood  loses  all  the  carbon  dioxide  not 
■only  from  the  acid  but  also  from  the  neutral  carbonates, 
because  it  contains  substances  of  a  weak  acid  character, 
which  drive  the  carbon  dioxide  out  of  its  union  with  alkalies. 
These  substances  are  the  proteids  and  the  haemoglobin. 

The  nitrogen  of  the  blood  is  only  physically  dissolved. 
The  per  cent  of  gases  in  the  blood  is : 

Arterial  Blood.  Venous  Blood. 

Oxygen 19.2  vol.  <?o  1 1.9  vol.  fo 

Carbon  dioxide 39.5       "  45-3      " 

Nitrogen 2.7      "  2.7      " 

These  volumes  of  the  gases  are  measured  at  o°  C.  and  760  mm 
mercury  pressure.  The  amount  of  oxygen  in  the  arterial  blood  is 
below  that  of  saturation.  By  means  of  violent  artificial  respiration, 
the  amount  of  oxygen  can  be  brought  to  23^.  The  venous  blood 
is  not  half  saturated  with  carbon  dioxide. 

Arterial  blood  is  bright  red;   venous  blood,  dark  red. 

The  difference  in  color  of  arterial  and  venous  blood  is  due  to 
the  difference  in  oxygen  present.  Artificially  we  can  change 
arterial  blood  to  dark  red  by  taking  away  its  oxygen  (shaking  with 
gases  free  of  oxygen),  and  venous  to  a  bright  red  by  shaking  with 
oxygen. 

When  arterial  blood  becomes  venous,  the  concentration  and 
alkalinity  of  the  plasma  are  increased,  for  the  following  reasons : 
The  red  blood  corpuscles  swell  by  the  inhibition  of  water  from  the 
plasma,  leaving  the  plasma  more  concentrated.  By  the  mass 
action  of  the  carbonic  acid,  hydrochloric  acid  is  set  free  from  the 
sodium  chloride;  this  hydrochloric  acid  enters  the  blood  cor- 
puscles, while  the  alkali  carbonate  remains  behind.  When  blood 
is  rendered  arterial,  the  opposite  takes  place. 

Venous  blood  is  found  in  the  veins  (except  pulmonary 
vreins),    in    the    right   heart   and    in    the    pulmonary   artery; 


60  HUMAN  PHYSIOLOGY 

arterial  blood  is  found  in  the  arteries  (except  pulmonary 
artery),  the  left  heart,  and  the  pulmonary  veins.  The 
change  from  venous  to  arterial  blood  is  brought  about  by  the 
taking  up  of  oxygen  and  the  giving  off  of  carbon  dioxide  in 
the  lungs — pulmonary  respiration.  The  change  from  arterial 
to  venous  blood  is  brought  about  by  the  giving  off  of  oxygen 
and  the  taking  up  of  carbon  dioxide  in  the  tissue — tissue 
respiration. 

>.    PULMONARY    RESPIRATION 

The  exchange  of  gases  between  the  blood  and  the  air  of 
the  lungs  depends  upon  the  diffusion  of  gases  through  the 
walls  of  the  alveoli  and  capillaries.  This  diffusion  takes 
place  from  places  of  higher  to  places  of  lower  gas  pressure. 

The  inhaled  or  exhaled  air  contains  the  following  gases: 

Inspired  Air.  Expired  Air. 

Nitrogen 79.00  vol.  fo  80.0  vol.  fo 

Oxygen 20.96      "  16.0 

Carbon  dioxide 0.04      "  4.0 

The  partial  pressure  at  760  mm  Hg  is: 

Inspired  Air.  Expired  Air. 

Oxygen 152  mm  Hg       122  mm  Hg 

Carbon  dioxide 0.3         "  30 

The  pressure  or  tension  of  the  gases  of  the  blood  is  stated 
in  terms  of  the  partial  pressure  of  these  gases  in  a  vessel 
containing  the  blood,  necessary  to  keep  the  quantity  of  the 
gases  in  the  blood  constant.      The  tension  is: 

Arterial  Blood.  Venous  Blood. 

Oxygen 29.6  mm  Hg      21.0  mm  lli^ 

Carbon  dioxide 22.0        "  41. 0 

The  partial  pressure  of  oxygen  in  inspired  air  is  larger 
than  its  tension  in  the  venous  blood;  that  of  carbon  dioxide 
is  less.  Therefore  an  exchange  of  gases  between  the  blood 
and  the  air  in  the  lungs  takes  place  by  diffusion  through  the 
walls  of  the  alveoli  and  of  the  capillaries. 


THE   GASES   OF   THE  BLOOD  61 

According  to  some  authors,  the  parenchyma  of  the  lungs  plays 
an  active  part  in  the  giving  off  of  carbon  dioxide  (in  the  same 
manner  as  gland  cells  in  the  secretion). 

The  lowest  barometric  pressure  at  which  respiration  of  the  quiet 
body  can  continue  undisturbed  is  about  350  mm  Hg. 

The  oxygen  taken  up  by  the  blood  favors  the  giving  off 
of  carbon  dioxide  because  by  it  the  carbon  dioxide  tension 
is  increased,  owing  to  the  fact  that  oxyhemoglobin  is  more 
acid  than  reduced  haemoglobin. 

An  adult  man  inhales  in  24  hours  about  700  g  or  500 
litres  of  oxygen  and  exhales  900  g  or  450  litres  of  carbon 
dioxide. 

The  ratio  of  the  volume  of  the  exhaled  carbon  dioxide  to  the 
volume  of  the  inhaled  oxygen  is  called  the  respiratory  quotient. 
Concerning  its  value  under  various  circumstances  see  Chapter  XII. 

Besides  the  lungs,  the  skin  also  throws  off  carbon  dioxide  in 
small  amounts  (8.4  g  per  day). 

3.   TISSUE    RESPIRATION 

This  consists  of  the  giving  off  of  oxygen  by  the  blood  to 
the  tissues  and  the  taking  up  of  carbon  dioxide.  This  takes 
place  in  the  systemic  capillaries.  The  giving  off  of  oxygen 
takes  place  because  the  oxygen  tension  in  the  blood  is 
greater  than  that  in  the  tissues.  Because  of  the  continual 
oxygen  consumption,  the  oxygen  tension  in  the  tissues  is  o. 
The  carbon  dioxide  formed  by  the  combustion  of  the  tissues 
accumulates  to  such  an  extent  that  its  pressure  is  higher  than 
that  of  the  carbon  dioxide  in  the  arterial  blood,  hence  it 
must  pass  into  the  blood. 

The  physiological  combustion,  by  which  oxygen  of  the  blood  is 
consumed  and  carbon  dioxide  produced,  does  not  take  place  in 
the  blood,  but  in  the  tissue.     This  is  based  on  the  following  facts: 

1.  The  extent  of  the  physiological  combustion  is,  up  to  a  certain 
limit,  independent  of  the  amount  of  blood  in  the  body.  After  a 
considerable  loss  of  blood,  warm-blooded  animals  show  no  change 
in  the  amount  of  oxygen  consumed  and  the  carbon  dioxide  formed, 
and  in  cold-blooded  animals  (frog)  the  physiological  combustions 
can  take  place  when  all  their  blood  has  been  taken  awav  and 
replaced  by  an  injected  physiological  salt  solution. 


62  HUMAN  PHYSIOLOGY 

2.  If  the  processes  of  combustion,  upon  which  the  contraction 
and  work  of  muscles  depend,  took  place  in  the  capillary  blood  of 
the  muscle,  the  muscle  fibre  would  be  forced  to  do  its  work  by 
transforming  the  heat,  supplied  to  it  from  the  blood,  into 
mechanical  work.  By  heating  the  muscle  fibre,  however,  we  are 
not  able  to  obtain  as  powerful  contractions  as  by  physiological 
stimulation,  if  we  do  not  use  temperatures  which  destroy  the  life 
of  the  muscle  (see  heat-rigor,  Chapter  XIV).  Besides  this, 
muscles  from  which  the  blood  has  been  removed  by  injecting 
physiological  salt  solutions,  and  even  isolated  muscles,  can,  by 
stimulation,  be  made  to  contract. 


CHAPTER    IV 
CIRCULATION    OF    BLOOD 

1.   INTRODUCTION 

i.  If  the  blood  is  to  fulfill  its  function  of  carrying- 
materials  between  the  organs  of  the  body,  it  must  circulate 
in  the  vascular  system. 

.2.  The  blood  flows  from  the  left  ventricle  through  the 
aorta  and  systemic  arteries  to  the  capillaries,  and  from  these 
through  the  veins  and  right  auricle  to  the  right  ventricle; 
thence  through  the  pulmonary  artery,  capillaries,  and  veins 
and  through  the  left  auricle  back  to  the  left  ventricle 
(Harvey,   1628). 

The  portal  vein,  formed  from  the  capillaries  of  the  intestine, 
branches  again  into  capillaries  in  the  liver,  which  in  turn  give  rise 
to  the  hepatic  veins. 

3.  The  difference  in  blood  pressure  in  the  different  parts 
of  the  vascular  system  is  the  cause  of  the  circulation  of  the 
blood.  The  blood  is  driven  from  places  of  higher  to  those 
of  lower  pressure. 

4.  The  differences  in  pressure  are  caused  by  the  rhythmic- 
ally contracting  ventricles  which,  during  their  contraction 
(systole)  empty  their  contents  into  the  aorta  and  pulmonary 
artery  and,  during  their  relaxation  (diastole),  take  the  blood 
from  the  auricles  and  veins. 

5.  The  valves  of  the  heart  prevent  the  regurgitation  of  the 
blood  from  the  ventricles  into  the  veins  and  from  the  arteries 
into  the  ventricles  and  thereby  determine  the  flow  of  blood 
in  one  direction. 

63 


64  HUMAN   PHYSIOLOGY 

•2.   THE    HEART 

i .  The  structure  of  the  heart. — The  heart  is  a  hollow 
muscle,  divided  by  a  partition  into  two  cavities,  the  left  and 
the  right  heart.  Its  cavity  consists  of  a  thin-walled  auricle 
and  a  thick-walled  ventricle.  The  muscle  fibres  inclose  the 
cavities  in  different  directions,  some  more  or  less  obliquely, 
some  in  the  form  of  the  figure  8,  some  circularly.  The  \valls 
of  the  left  ventricle  are  thicker  than  those  of  the  right 
ventricle. 

At  the  boundary  between  the  auricle  and  the  ventricle  are 
found  the  auriculo-ventricular  valves,  on  the  right  side  three 
(tricuspid)  and  on  the  left  two  (bicuspid)  membranes  hang- 
ing down  into  the  ventricle.  On  the  free  edges  of  these 
membranes  are  the  corda;  tendinea,-,  which  are  connected 
with  the  wall  of  the  ventricle  by  the  papillary  muscles. 

Between  the  left  ventricle  and  the  aorta  and  between  the 
right  ventricle  and  the  pulmonary  artery  are  the  three 
pocket-like  semi-lunar  valves ;  the  openings  of  the  pockets 
are  toward  the  arteries. 

2.   Properties  of  cardiac  muscle. 

For  the  investigation  of  the  physiological  properties  of  the 
cardiac  muscle,  the  excised  apex  of  the  frog's  heart  is  especially 
adapted,  as  this  contains  no  ganglionic  cells. 

The  heart  muscle-fibre  is  cross-striated,  but  differs  from  the 
striated  skeletal  muscle  in: 

(a)  Its  structure.      The  cardiac   muscle-fibres  branch   and  anas- 
tomose with  each  other. 
(/-)  Its  functions: 

a.  A  stimulation,  if  at  all  active,  always  calls  forth  a 
maximum  contraction  of  the  cardiac  muscle,  while  a 
skeletal  muscle  does  not  give  a  maximum  contraction  with  a 
weak  stimulation. 

(i.  The  cardiac  muscle  can  be  thrown  into  tetanus  only 
under  certain  abnormal  conditions.  If  the  cardiac  muscle 
is  continuously  stimulated,  e.g.  by  a  constant  current  or  by 
tetanizing  induction  shocks,  generally  no  lasting  contrac- 
tion takes  place  (as  in  the  skeletal) ;  but  the  heart  makes 
rhythmical  single  contractions  which  at  best  fuse  into  an 
incomplete  tetanus  (an  irregular  agitation  and  heaving  of  the 
muscle). 


CIRCULATION  OF  BLOOD  65 

y.  During  its  contraction  the  cardiac  muscle  is  not 
irritable  (refractive)  from  the  beginning  to  the  maximum  of 
the  contraction.  During  this  time  a  stimulation  is  inactive. 
In  its  relaxed  condition,  the  cardiac  muscle  is  again  irritable; 
if  a  stimulus  is  introduced  during  this  stage,  a  new  contrac- 
tion occurs  which  is  the  greater  in  proportion  as  the  stimu- 
lation occurs  later.  When,  in  an  independent  rhythmically 
beating  heart,  such  an  "  extra  contraction"  is  called  forth 
by  an  artificial  stimulus  during  the  diastole,  the  pause  fol- 
lowing upon  this  contraction  and  lasting  to  the  next  inde- 
pendent beat  is  longer  than  the  ordinary  pause  between  two 
independent  beats.  This  lengthened  pause  is  called  the 
compensatory  pause. 

The  physiological  contractions  of  the  cardiac  muscle  con- 
sist of  single  contractions  which  follow  each  other  in  a 
definite  rhythm.  The  contraction  is  called  systole,  and  the 
relaxation  following  upon  it  is  called  diastole. 

The  contraction  of  the  heart  begins  at  the  mouth  of  the 
veins,  from  these  it  travels  through  the  walls  of  the  auricle 
and  then  through  the  walls  of  the  ventricle.  The  whole 
cardiac  cycle  lasts  about  0.86  second,  which  may  be  divided 
as  follows : 

1.  Auricular  systole  (ventricles  at  rest),  0.16  second. 

2.  Ventricular  systole  (auricles  at  rest),  0.3  second. 

3.  Pause,  during  which  both  auricles  and  ventricles  are 
at  rest,  0.4  second. 

The  number  of  heart-beats  in  one  minute  in  an  adult 
human  being  is  on  the  average  70 ;  in  children  it  is  higher 
(first  year  134)  ;  the  number  is  increased  by  increase  of  tem- 
perature (fever),  muscular  exertion,  after  the  taking  up  of 
food;   it  depends  also  upon  mental  conditions. 

The  contraction  of  the  ventricular  or  auricular  wall  does  not 
occur  at  all  points  simultaneously,  but  spreads  itself  along  the 
cardiac  muscle,  like  the  contraction  waves  in  the  fibres  of  skeletal 
muscles.  This  is  proven  by  the  fact  that  the  electrical  phenomena 
of  the  stimulated  cardiac  muscle  dc  not  appear  simultaneously  at 
all  points,  so  that  it  is  possible  to  demonstrate,  as  in  the  striated 
skeletal  muscle,  a  current  of  action.  (See  Chapter  XIV.)  From 
the  results  of  the  electrical  phenomena  it  can  also  be  concluded 
that  the  cardiac  contraction  corresponds  to  a  twitch  and  not  to  a 
short  tetanus. 


66  HUMAN  PHYSIOLOGY 

The  heart  contains  within  itself  the  processes  which 
stimulate  it  to  its  rhythmic  activity,  for  it  beats  for  some 
time  after  it  has  been  cut  out  of  the  animal  immediately  after 
death.  Concerning'  the  nature  of  this  stimulation  nothing 
is  known. 

Perhaps  the  cardiac  muscle  is  stimulated  directly  by  the 
normal  stimulus  and  not  through  the  intervention  of  the 
sraneflionic  cells  and  nerve-fibres  found  in  the  walls  of  the 
heart. 

In  the  mammalian  heart  the  ganglionic  cells  lie  in  the  auriculo- 
ventricular  groove,  in  the  partition  between  the  auricles,  and  in  the 
auricle  near  the  mouth  of  the  superior  vena  cava.  Their  function 
is  not  known. 

The  embryonic  heart  has  no  ganglia  and  yet  beats  rhythmically ; 
in  that  case  the  cause  of  the  rhythmic  activity  must  certainly  lie 
in  the  muscle  itself. 

Concerning  the  influence  of  the  central  nervous  system 
upon  the  heart,  see  page  74. 

3.  The  circulation  of  the  blood  in  the  heart. 

(tf)  In  the  ventricle. — During  the  ventricular  systole,  the 
cavities  of  the  ventricles  are  reduced  in  size;  the  blood 
which  it  contains  is  pressed  out  into  the  aorta  and  pulmonary 
artery.  The  ventricles  do  not  completely  empty  themselves 
since,  even  in  the  strongest  contraction,  the  cavities  of  the 
heart  are  not  entirely  obliterated. 

The  auriculo-ventricular  valves  which  float  upon  the  blood 
during  the  ventricular  diastole  are  closed  during  the  ventric- 
ular systole  so  that  the  blood  cannot  regurgitate  into  the 
auricle.  When  the  pressure  in  the  ventricle  is  increased  by 
the  systole,  the  blood  flows  behind  the  valves  and  presses 
their  surfaces  together  so  that  they  are  completely  closed. 
The  valves  do  not  bulge  into  the  auricles  because  they  are 
fastened  to  the  papillary  muscles  which  contract  simultane- 
ous!}' with  the  walls  of  the  ventricle. 

The  closure  of  the  valves  seems  to  follow  the  beginning 
of  the  systole  so  quickly  that  no  blood  whatever  re-enters 
the  auricle. 

During  the  ventricular  diastole  the  blood  does   not  flow 


CIRCULATION   OF  BLOOD  67 

back  from  the  arteries,  as  it  accumulates  in  the  pockets  of 
the  semi-lunar  valves,  pressing  their  surfaces  together  and 
thus  closing  them.  The  pressure  in  the  ventricle  after 
diastole  becomes  less  than  that  in  the  auricle,  so  that  now 
the  blood  flows  from  the  auricle  into  the  ventricle,  after 
having  opened  the  auriculo-ventricular  valves. 

(J?)  In  the  auricles. — The  contraction  of  the  auricle  serves 
chiefly  to  regulate  the  flow  in  the  large  veins.  During  the 
ventricular  systole  when  no  blood  is  allowed  to  pass  from 
the  auricle  into  the  ventricle,  it  flows  from  the  veins  into  the 
dilating  auricle.  When,  during  ventricular  pause,  it  is 
streaming  into  the  ventricle,  the  auricle  decreases  in  size 
proportionately  to  its  decrease  in  contents. 

4.  The  pressure  in  the  heart. 

For  finding  the  pressure  in  animals,  a  long  canula  is  pushed 
either  through  one  of  the  large  cervical  vessels  into  the  right 
auricle  or  ventricle,  or  through  the  carotid  into  the  left  ventricle. 
The  canula  is  connected  with  an  instrument  for  measuring  the 
pressure  (mercury  or  spring  manometer).  The  extent  of  the 
pressure  is  indicated  by  the  number  of  millimeters  of  mercury 
which  it  stands  above  the  atmospheric  pressure. 

During  the  systole  the  pressure  in  the  ventricles  increases 
rapidly  at  first  and  then  more  slowly.  In  the  left  ventricle 
it  reaches  a  height  of  200,  in  the  right  ventricle,  60  mm  Hg. 
During  diastole  the  pressure  sinks  rapidly  and  may  become 
negative,  but  before  the  next  systole  occurs  it  rises  a  little 
because  of  the  incoming  blood. 

The  period  of  preparation  lasts  from  the  beginning  of  the 
ventricular  systole  (or  the  closing  of  the  auriculo-ventricular 
valves)  to  the  opening  of  the  semi-lunar  valves;  it  amounts  to 
0.05-0.1  second.  It  can  be  estimated  in  animals  by  registering 
simultaneously  the  pressure  in  the  left  ventricle  and  in  the  aorta; 
the  semi-lunar  valves  open  the  moment  the  ventricular  pressure 
becomes  greater  than  the  aortic.  In  man,  the  length  of  this 
period  has  been  found  by  comparing  the  cardiac  impulse  and  the 
pulse  curve. 

The  period  of  discharge  is  the  period  from  the  opening  to  the 
closing  of  the  semi-lunar  valves;  during  this  time  the  ventricular 
pressure  is  higher  than  that  of  the  aorta;  length  of  period 
0.18—0.20  second. 


68  HUMAN  PHYSIOLOGY 

In  the  auricle  the  variations  in  pressure  are  much  less  than 
in  the  ventricles.  During'  the  auricular  systole  the  highest 
pressure  is  20  mm  Hg. 

5.  The  cardiac  sounds,  produced  by  the  contraction  of 
the  heart,  are  heard  when  the  ear  is  applied  to  the  chest- 
wall. 

The  first  sound,  produced  during  the  ventricular  systole, 
is  dull,  lasts  as  long  as  the  systole,  and  can  be  best  heard 
over  the  ventricle.  It  depends  upon  the  muscle  tone  (see 
Chapter  XIV)  and  upon  the  vibration  of  the  auriculo-ven- 
tricular  valves  produced  by  the  sudden  systolic  contraction. 
It  is  still  audible  in  the  bloodless  heart. 

The  second  sound  is  short,  clear,  and  most  distinct  over  the 
aorta ;  it  is  caused  by  the  vibration  of  the  semi-lunar  valves 
produced  by  their  sudden  closure. 

6.  The  cardiac  impulse,  or  apex  beat,  is  synchronous  with 
the  contraction  of  the  heart  and  is  felt  at  the  fourth  or  fifth 
intercostal  space,  about  one  and  one-half  inches  to  the  left  of 
the  sternum.  It  is  produced  mainly  as  follows:  the  tensely 
contracted  cardiac  muscle  at  this  point  pushes  forward  the 
soft  part  of  the  intercostal  space;  during  the  relaxation  of 
the  heart,  this  part  is  pushed  inward  by  the  atmospheric 
pressure. 

Other  factors,  supposed  to  play  a  part  in  the  formation  of  the 
cardiac  impulse,  are  the  following: 

During  the  systole,  the  apex  of  the  heart  is  raised  upward; 
during  the  discharging  of  the  blood,  upward  and  backward,  the 
heart  is  pushed  forward  and  downward;  the  arterial  trunks,  from 
which  the  heart  is  suspended,  when  filling  are  slightly  twisted  and 
when  emptying  untwisted  from  their  spiral-like  turning. 

If  a  button  [pelotte]  is  fixed  upon  the  place  of  cardiac  impulse, 
so  that  it  is  moved  by  the  beat  of  the  heart,  and  if  this  movement 
is  transferred  to  a  writing-lever,  this  lever  will  describe  a  curve 
called  the  cardiogram.  This  cardiogram  is  similar  to  the  pressure 
curve  of  the  heart,  as  it  is,  in  reality,  produced  by  the  contraction 
of  the  cardiac  muscle;  the  two  curves  are,  however,  not  identical, 
since  the  cardiogram  represents  a  pressure  and  volume  curve. 

7.  The  work  of  the  heart. — The  work  which  the  heart 
does  during  one  contraction  is  equal  to  the  product  of  the 


CIRCULATION   OF  BLOOD  69 

■weight  by  the  height  to  which  the  weight  is  carried.  The 
weight  lifted  is  that  of  the  amount  of  blood  sent  by  a  single 
systole  of  the  heart  (pulse  volume).  The  amount  of  blood 
thus  lifted  is  about  66  cc,  and  its  weight  0.07  kg.  The 
height  to  which  this  is  raised  is  equal  to  the  blood  pressure 
in  the  aorta  or  in  the  pulmonary  artery.  In  the  aorta  the 
pressure  is  about  1  50  mm  of  mercury  or  about  two  metres 
of  blood ;  in  the  pulmonary  artery,  the  pressure  is  about  one- 
third  of  that  in  the  aorta.  During  one  contraction,  the  left 
ventricle,  therefore,  does  the  work  of  0.07  X  2  or  0.14  kilo- 
grammetre,  the  right  ventricle  0.047.  In  all,  the  heart  in 
twenty-four  hours  does  about  18,000  kilogrammetres  of  work. 

The  pulse  volume  is  estimated  by  many  authors  as  much  greater 
(up  to  180  cc)  and  then  the  work  done  is  correspondingly  greater. 

In  this  calculation,  no  account  is  taken  of  the  work  which  the 
heart  does  in  imparting  velocity,  i.e.  kinetic  energy,  to  the  blood 
(about  0.3  m  per  second).  But  this  work  is  very  little  compared 
with  that  done  to  overcome  the  blood  pressure,  the  former  not 
being  more  than  \fc  of  the  latter. 

3.    CIRCULATION    OF    THE    BLOOD    IN    THE    VESSELS 

1.  The  blood  pressure  in  the  vessels. — The  blood  pres- 
sure is  the  pressure  of  the  blood  upon  the  walls  of  the 
vessels,  this  determining  the  tension  of  the  walls. 

The  blood  pressure  in  the  larger  vessels  is  measured  by  inserting 
a  canula  into  the  vessel  and  connecting  this  canula  with  a  register- 
ing manometer.  The  pressure  can  also  be  determined  without 
any  operation  in  many  blood  vessels  of  man,  it  being  equal  to  the 
pressure  necessary  to  close  these  vessels.  An  artery  is  closed  when 
no  pulse  is  felt  peripheral  to  the  compression.  The  capillarv 
pressuie  is  found  by  pressing  upon  a  glass  plate,  placed  on  the  red 
part  of  the  skin,  till  the  skin  becomes  pale. 

The  blood  pressure  in  different  parts  of  the  vascular  system 
varies  greatly.  The  difference  in  pressure  is  produced  by 
the  activity  of  the  heart  and  is  the  cause  of  the  movement  of 
the  blood.  Each  particle  of  blood  is  forced  from  a  place  of 
higher  to  a  place  of  lower  pressure. 

The  blood  pressure  constantly  decreases  as  we  proceed 


70  HUMAN  PHYSIOLOGY 

from  the  aorta  or  pulmonary  artery,  through  the  arteries, 
capillaries,  and  veins,  to  the  heart.  The  blood  must  conse- 
quently flow  in  this  direction.  By  this  movement  of  the 
blood,  the  difference  in  pressure  is  normally  not  entirely 
equalized,  because  by  each  succeeding  ventricular  systole 
the  difference  in  pressure  is  increased. 

In  the  aorta,  the  blood  pressure  undergoes  variations  of 
about  I  50  mm  Hg  ;  in  the  larger  arteries,  about  1  10-120  mm  ; 
in  the  capillaries,  24-54  mm  ;  in  the  veins,  only  a  few  mm, 
indeed  in  the  large  veins  in  and  near  the  thorax  it  may  be  a 
negative  pressure  of  a  few  mm,  i.e.  it  is  less  than  the  atmos- 
pheric pressure.  On  cutting  such  a  large  vein,  no  blood 
flows  from  the  vessel,  but  air  enters  it.  The  cause  of  this 
negative  pressure  in  the  veins  is  the  negative  pressure  exist- 
ing in  the  thoracic  cavity  which  is  increased  during  inspira- 
tion (see  Chapter  V).  The  blood  pressure  in  the  pulmonary 
artery  is  about  50  mm  Hg. 

The  blood  pressure  in  the  arteries  undergoes  periodic 
variations  caused  by  the  action  of  the  heart ;  these  variations 
are  called  the  pulse.  Each  time  that  the  ventricular  systole 
sends  blood  into  the  aorta  and  pulmonary  artery,  the 
pressure  in  these  vessels  is  suddenly  increased ;  after  this, 
the  streaming  of  the  blood  to  the  capillaries  causes  a  diminu- 
tion in  pressure.  This  periodic  variation  in  pressure  spreads 
itself  as  a  wave  throughout  the  whole  arterial  system. 

The  pulsatory  variations  in  pressure  are  the  largest  in  the 
aorta,  where  they  amount  to  half  of  the  average  pressure ; 
they  become  smaller  in  the  peripheral  arteries.  In  the 
capillaries  and  the  veins  there  is  normally  no  pulse. 

The  rate  of  the  pulse  wave  (not  to  be  confounded  with  the  rate 
of  the  blood  How)  can  be  found  by  determining  the  time  elapsing 
between  the  beginning  of  the  cardiac  impulse  and  the  appearance 
of  the  pulse  in  a  peripheral  artery.  The  rate  is  about  six  metres 
in  one  second;  it  depends  upon  the  tension  and  the  elasticity  of 
the  arterial  walls.       The  length  of  the  pulse  wave  is  about  1.5  m. 

If  a  lever  is  placed  upon  an  artery  so  that  it  is  moved  by  the 
pulsating  artery,  and  if  this  movement  is  transferred  to  ami  mag- 
nified by  a  writing  lever,  a  curve,  the  pulse  curve,  or  sphygmogram, 


CIRCULATION   OF  BLOOD  71 

is  produced.  This  curve  describes  more  accurately  the  progress 
of  the  pulse.  The  apparatus  for  the  production  of  a  pulse  curve 
is  called  a  sphygmograph. 

The  pulse  curve   (Fig.    i)  ascends  rapidly  and  then  sinks 
more  slowly  to  the  level  of  the  abscissa.      In  the  descent  of 


Fig.   i. — Pclse  Curve  (Sphvgmogram)  of  the  Radial  Artery. 

the  curve  there  is  regularly  found  a  small  elevation,  called 
the  dicrotic  wave.  The  cause  of  this  wave  is  not  fully 
known.  Often  the  descending  part  of  the  curve  shows  still 
other  smaller  elevations  which  are  supposed  to  be  due  to  the 
reflection  of  the  pulse  wave  in  the  various  parts  of  the  arterial 
system. 

The  blood  pressure  shows  other  periodic  variations  which  are 
synchronous  with  the  respiratory  movements;  the  pressure  sinks 
during  inspiration  and  rises  during  expiration.  This  is  chiefly 
due  to  the  fact  that  during  inspiration  the  introthoracic  pressure 
and  therefore  the  pressure  upon  the  blood  vessels  in  the  thorax  is 
diminished,  while  during  expiration  it  is  increased.  Hence  the 
blood  vessels  in  the  thorax  are  better  filled  with  blood  during 
inspiration  than  during  expiration. 

In  general  the  amount  of  blood  pressure  and  its  pulsatory 
variations  depend  upon  the  state  of  fulness  of  the  vessels, 
the  tonus  of  the  muscles  of  the  blood  vessels,  and  upon  the 
number  and  strength  of  the  cardiac  contractions. 

2.  Rate  of  blood  flow. — In  the  arteries  the  blood  flows 
with  a  periodically  accelerating  rate  (corresponding  to  the 
intermittent  entrance  of  blood  into  the  aorta) ;  in  the  capil- 
laries and  veins  the  flow  is  uniform.  The  change  from  the 
intermittent  movement  of  the  blood  in  the  arteries  to  the 
uniform  movement  in  the  capillaries  is  due  to  the  extensi- 
bility and  elasticity  of  the  arterial  walls.  In  vessels  with 
rigid  walls,  each  systole  must  force  forward  the  column  of 
blood  previously  pressed  out  of  the  heart.  In  vessels  with 
elastic  walls,  the  force  of  the  systole  is  not  directly  trans- 
formed into  the  movement  of  the  blood,  but  is  first  changed 
to  the  increased  tension  of  the  elastic  walls,  and  this  stored- 


72  HUMAN  PHYSIOLOGY 

up  energy  is  then  gradual ly  transformed   into  the  energy  of 
the  moving  blood.      This  causes  the  flow  to  be  continuous. 

The  change  of  the  intermittent  into  the  continuous  movement 
occurs,  according  to  the  same  principle,  in  the  fire-engine.  The 
water  which  enters  the  engine  periodically,  leaves  it  in  a  contin- 
uous stream,  being  pressed  out  continuously  by  the  compressed 
air  in  the  air-chamber. 

The  average  velocity  decreases  as  we  proceed  from  the 
arteries  to  the  capillaries,  and  increases  again  from  the  capil- 
laries to  the  veins.  In  the  large  arteries  the  rate  is  200-400 
mm  per  second;  in  capillaries  0.6-0.8  mm;  in  the  large 
veins  it  is  but  little  less  .than  in  the  arteries.  The  cause  of 
this  difference  is  the  difference  in  the  total  cross-section  of 
the  various  parts  of  the  vessels.  Through  each  total  cross- 
section  of  the  vascular  system  there  must  pass  in  the  same 
unit  of  time  the  same  quantity  of  fluid,  in  order  that  the  flow 
shall  not  become  stationary  and  the  blood  collect  in  one 
place.  Now  the  cross-section  of  the  aorta  and  the  large 
veins  is  much  less  than  the  total  cross-section  of  all  the 
capillaries.  As  the  rate  is  equal  to  the  volume  flowing 
through  in  one  second  divided  by  the  cross-section,  it  is 
evident  that  the  rate  in  the  arteries  and  veins  must  be 
greater  than  that  in  the  capillaries. 

The  rate  in  the  larger  vessels  of  animals  is  found  in  the  follow- 
ing manner.  A  blood  vessel  is  cut  and  between  the  cut  ends  a 
sufficiently  wide  tube,  the  contents  of  which  have  been  accurately 
determined,  is  inserted.  The  blood  must  now  pass  through  the 
tube.  The  time  taken  by  the  blood  to  pass  from  one  end  of  the 
tube  to  the  other  is  then  determined.  For  this  experiment,  the 
tube  is  previously  filled  with  some  indifferent  fluid,  which  is  forced 
from  it  into  the  vascular  system  by  the  incoming  blood.  Accord- 
ing to  this  principle,  the  haemodromometer  of  Volkmann  is  built, 
as  is  also,  though  more  complicated,  the  Stromuhr  of  Ludwig. 

In  the  capillaries  the  distance  traversed  by  a  blood  corpuscle  is 
measured  direct]}-  with  the  aid  of  a  microscope  (e.g.  in  the  web  of 
frog's  foot). 

The  pulsatory  changes  in  the  rate  of  the  arterial  blood  can  be 
investigated  by  the  plethysmography  an  apparatus  registering  the 
changes  in  the  pulse-volume  of  a  limb.  The  changes  in  volume 
are   due  tu   the   periodic   increase  and    decrease   in    the   supply  of 


CIRCULATION  OF  BLOOD  73 

blood  to  the  arteries  of  the  limb,  as  the  outflow  of  blood  into  the 
veins  is  uniform. 

3.  The  resistance  to  moving   blood  due   to   friction. — 

The  energy  of  the  moving"  blood  must  overcome  the  resist- 
ance due  to  the  friction  of  the  particles  of  blood  upon  each 
other  and  upon  the  walls  of  the  vessels.  The  friction  is 
greater  the  smaller  the  cross-section  of  the  vessel. 

In  a  given  cross-section  of  a  blood  vessel,  all  the  parts  of 
the  blood  do  not  move  with  the  same  velocity,  but  those  in 
the  middle  of  the  vessel  move  faster,  while  those  touching 
the  walls  move  slowest;  this  is  due  to  the  resistance  caused 
by  friction.  In  the  swifter  axial  current  float  the  specifically 
heavier  particles  of  the  blood,  the  red  blood  corpuscles ;  in 
the  slower  peripheral  stream  are  found  the  lighter  leucocytes. 

4.  Relation  between  fall  in  pressure,  rate  of  flow  and 
resistance. — The  energy  is  used  for  producing  movement 
and  for  overcoming  resistance ;  its  consumption  is  the 
greater,  the  greater  the  movement  produced  and  the  greater 
the  resistance  overcome.  The  amount  of  energy  consumed 
in  a  given  length  of  vessel  is  measured  by  the  decrease  in 
pressure.  The  decrease  in  pressure  in  a  unit  of  distance  is 
called  the  fall. 

In  a  tube  of  uniform  diameter,  in  which  the  resistance  offered 
by  every  cross-section  is  the  same,  and  in  which  the  rate  of  flow 
is  the  same  at  all  cross-sections,  the  decrease  in  pressure  is  pro- 
portional to  the  distance  traversed,  i.e.  the  fall  is  uniform  through- 
out. But  if  the  fluid  flows  through  a  tube  of  non-uniform  bore, 
the  fall  in  the  wider  portions  will  be  less  than  in  the  narrower 
parts,  because  in  the  wider  parts  the  resistance  is  less. 

The  question  where  the  fall  is  greatest  cannot  be  definitely 
answered.  In  the  vascular  system  the  total  cross-section 
increases  as  we  proceed  from  the  arteries  to  the  capillaries, 
but  the  cross-section  of  the  individual  vessel  decreases ;  going 
from  the  capillaries  to  the  veins,  it  is  the  reverse.  Now  the 
resistance  is,  on  the  one  hand,  the  smaller  the  greater  the 
total  cross-section;  but,  on  the  other  hand,  the  greater  the 
smaller  the  individual  cross-section.      Of  these  two  opposing 


74  HUMAN   PHYSIOLOGY 

variations  in  resistance,  the  decrease  predominates  in  the 
larger  arteries,  while  the  increase  predominates  in  the  veins, 
so  that  in  the  larger  arteries  the  fall  is  but  little;  in 
the  veins,  large.  In  regard  to  the  extent  of  the  fall  in 
the  smaller  arteries  and  capillaries,  the  evidences  are  con- 
flicting. 

5.  Valves  in  the  veins. — The  circulation  of  blood  in  the 
veins  is  aided  by  externally  compressing  them,  as  occurs  by 
the  contraction  of  surrounding  muscles;  the  regurgitation  of 
the  blood  is  prevented  by  valves,  somewhat  like  the  semi- 
lunar valves,  which  allow  the  blood  to  flow  in  the  direction 
toward  the  heart  only. 
6.   Circulation  time. 

To  determine  the  time  of  a  complete  circulation  ferrocvanide 
•  if  potassium  is  injected  into  the  central  end  of  a  severed  vein,  the 
time  of  injection  being  noticed.  After  some  time  the  blood  from 
the  peripheral  end  of  the  cut  vein  is  tested  for  the  salt  by  being 
colored  blue  with  ferric  chloride.  The  blood  has  completed  the 
entire  circulation  when  the  salt  reappears  at  the  peripheral  end  of 
the  vein. 

In  dogs  the  circulation  time  has  been  found  to  be  fifteen 
seconds,  in  man  it  is  supposed  to  be  twenty-two  seconds. 

4.    INNERVATION   OF    THE    ORGANS  OF   CIRCULATION 

The  influence  of  the  central  nervous  system  on  the  organs 
of  circulation  (heart  and  muscles  of  vessels)  serves  to  regu- 
late the  general  velocity  and  distribution  of  the  blood  to  the 
different  parts  of  the  body.  This  is  brought  about  by 
changes  in  the  number  and  strength  of  heart-beats  and  by 
changes  in  the  tonus  of  the  muscles  of  the  vessels,  especially 
of  the  arteries. 

1.   Innervation  of  the  heart  (see  also  page  66). 

(a)  The  cardiac  inhibitory  nerves  are  the  two  vagi  from 
which  fibres  for  the  cardiac  plexus  are  derived.  Section  of 
the  vagi  results  in  increasing  the  pulse  frequency.  The 
cardiac  vagi  are  therefore  continual ly  stimulated  (tonic). 
Stimulation  of  the  peripheral  end  of  a  cut  vagus  causes  a 
diminution    in    rate    and    strength    of   heart-beat    or    entire 


CIRCULATION   OF  BLOOD  75 

stoppage    of   the    heart    in    diastole,     depending    upon    the 

strength   of  the  stimulation.      How  the   action   of  the  vagus 

on  the  cardiac  muscle  is  brought  about  is  not  known. 

Pathological-anatomical  changes  have  been  observed  in  the 
cardiac  muscle  (atrophy  and  degeneration)  after  section  of  vagus. 

The  centre  for  the  cardiac  inhibitory  nerves  lies  in  the 
medulla  oblongata.  Its  activity  is  increased  by  lack  of 
oxygen  and  increase  of  carbon  dioxide  in  the  blood,  and  by 
increased  blood  pressure.  It  can  also  be  stimulated  in- 
directly by  stimulation  carried  to  it  by  centripetal  nerves 
from  the  cerebral  hemispheres. 

The  extent  of  its  activity  depends  also  upon  psychical  influences 
(palpitation  of  the  heart).  Reflex  cardiac  inhibition  takes  place 
if,  e.g.  in  a  frog,  the  sensory  nerves  of  the  abdomen  are  stimulated 
by  tapping  the  abdomen  (Goltz's  tapping  experiment). 

Atropin  and  curare  in  large  doses  destroy  the  action  of  the 
vagus  upon  the  heart;  muscarin  and  nicotin  stimulate  the  vagus 
endings  in  the  heart.  The  action  of  muscarin  is  neutralized  by 
atropin,  that  of  curare  by  nicotin.  Digitalin  stimulates  both  the 
vagus  endings  in  the  heart  and  the  centre  in  the  medulla. 

(p)  The  cardiac  accelerating  nerves  are  the  nervi  accel  >- 
rantes  which  pass  from  the  first  thoracic  and  the  cervical 
ganglia  of  the  sympathetic  to  the  cardiac  plexus.  Stimula- 
tion causes  increase  in  the  frequency  and  force  of  the  heart- 
beat. 

It  is  supposed  that  their  centre  lies  in  the  medulla 
oblongata,  and  that  this  is  also  tonic.  If  the  vagi  are  cut, 
electric  stimulation  of  the  medulla  causes  acceleration  of  the 
pulse. 

2.  Innervation  of  the  blood  vessels. — The  muscles  of  the 
vessels  (smooth  muscles;  are  most  developed  in  the  walls  of 
the  arteries,  less  in  the  veins.  The  walls  of  the  capillaries 
are  also  supposed  to  be  contractile,  but  this  is  independent 
of  the  nervous  system.  The  nervous  elements  for  the  muscles 
of  the  vessels  lie  partly  in  the  walls  of  the  vessels  themselves 
(ganglionic  cells,  nerve  plexus;  and  partly  enter  the  walls 
as  vaso-motor  nerves.  There  are  nerves  which  constrict 
and  nerves  which  dilate  the  blood  vessels. 


76  HUMAN  PHYSIOLOGY 

(a)  The  vaso-constrictor  nerves  have  their  centre  in  the 
medulla  oblongata,  extending  from  the  upper  part  of  the 
fourth  ventricle  to  the  lower  part  of  the  calamus  scriptorius, 
on  both  sides.  From  this  centre  the  nerve-fibres  proceed 
down  the  spinal  cord  and  connect  with  the  nerve-cells  of  the 
gray  matter;  from  there  the  fibres  pass  through  the  anterior 
roots  and  the  rami  communicantes  into  the  sympathetic.  The 
sympathetic  fibres  proceed  separately  (e.g.  splanchnic)  or 
with  other  peripheral  nerves  (e.g.  trigeminus,  sciatic)  to  the 
blood  vessels.  Some  vaso-motor  fibres  go  directly  to  the 
vessels  without  passing  through  the  sympathetic  (e.g.  from 
the  roots  of  the  lower  lumbar  and  of  the  sacral  nerves). 
The  vaso-motor  nerves  are  perhaps  not  in  direct  contact  with 
muscle  fibres,  but  pass  first  into  the  ganglionic  cells  of  the 
walls,  from  which  the  motor  fibres  proceed  to  the  muscles. 

The  vaso-motor  centre  is  tonic.  Section  of  a  vaso-motor 
nerve  causes  a  dilation  of  the  vessels  innervated  by  that 
nerve. 

If  the  cord  is  cut,  dilation  of  the  vessels  supplied  by  the 
sectioned  vaso-motor  nerves  results ;  but  eventually  the  tonus 
is  regained,  evidently  because  the  cells  in  the  spinal  cord, 
through  which  the  vaso-motor  nerves  pass,  have  assumed 
the  function  of  the  centre.  Even  after  section  of  a  peripheral 
vaso-motor  nerve,  the  tonus  is  eventually  regained ;  in  this 
case,  the  ganglionic  cells  in  the  walls  of  the  blood  vessels 
assume  the  role  of  the  centre. 

The  activity  of  the  vaso-motor  centre  is  influenced: 

i.    Directly  by  lack  of  oxygen   and  the  accumulation   of 
carbon    dioxide    in    the    blood ;     this    increases    its    action. 
Hence  asphyxia  stimulates  this  as  it  does  the  cardiac  inhibi- 
tory centre. 

2.    By  stimuli  conducted  to  it  through  the  nerves. 

[a)   Psychical   processes  can  increase  or  diminish  its: 
activity  (pallor  by  fear;   blushing). 

(/?)  The  activity  can  be  influenced  reflexively. 

We  classify  the  centripetal  nerves  used  in  this  reflex 
action  into: 


CIRCULATION  OF  BLOOD  77 

(a)  Pressor  nerves,  which  produce  a  strong  stimulation 
of  the  centre  and  a  constriction  of  the  vessels,  hence  an 
increase  in  blood  pressure. 

(/?)  Depressor  nerves,  i.e.  centripetal  nerves  which  re- 
flexively  inhibit  the  action  of  the  centre  and  thereby  cause 
■decreased  blood  pressure. 

Pressor  nerves  are  found,  e.g.  in  the  trigeminus,  superior 
and  inferior  laryngeal.  An  example  of  a  depressor  nerve  is 
the  depressor  nerve  going  from  the  heart  to  the  vagus  and 
thence  to  the  medulla ;  stimulation  of  this  nerve  causes  a 
lowering  of  the  blood  pressure,  and  decreases  the  rate  of 
heart-beat. 

(b)  The  vaso-dilator  nerves  produce  a  widening  of  the 
vessels  by  decreasing  the  tonus  of  their  muscles. 

Examples  of  vaso-dilator  nerves : 

i.  Through  the  chorda  tympani  there  pass  fibres  to  the 
submaxillary  salivary  glands ;  the  stimulation  of  this  nerve 
•causes  dilation  of  the  blood  vessels  of  the  gland. 

2.  Stimulation  of  the  nervi  erigentes  (fibres  passing  from 
the  sacral  plexus  to  the  hypogastric  plexus)  causes  accumula- 
tion of  blood  in  the  penis  and  thus  produces  erection. 

In  general  the  vaso-dilators  accompany  the  constrictor 
nerves.  In  these  cases  the  existence  of  the  two  kinds  of 
nerves  can  be  demonstrated,  as  they  possess  different 
irritability.  The  dilators  are  stimulated  by  a  weak,  slowly 
interrupted  electrical  current,  the  constrictors  need  a  stronger 
and  faster  interrupted  current. 

After  section,  the  dilators  retain  their  irritability  for  a  much 
longer  time  than  the  constrictors,  before  degeneration  sets  in. 

How  the  dilators  diminish  the  tonus  of  the  muscles  is  not 
known. 

It  is  supposed  that  the  centre  for  the  vaso-dilators  is  situated  in 
the  medulla. 

The  innervation  of  the  blood  vessels  serves  to  regulate  the 
distribution  of  the  blood  to  the  different  parts  of  the  body. 
This  distribution,  in  so  far  as  it  is  not  dependent  upon  pure 
mechanical    conditions,    is    regulated   by  the   tonus    of  the 


78  HUMAN   PHYSIOLOGY 

muscles  of  the  vessels  in  such  a  manner  that,  normally,  each 
part  of  the  body  contains  the  amount  of  blood  that  it  needs. 
The  more  active  a  certain  part  of  the  bod}-  is,  the  more 
►dilated  are  its  blood  vessels  and  the  greater  the  quantity  of 
blood  the)'  contain.  Simultaneously  with  the  dilation  in  an 
active  part,  there  is  a  constriction  in  the  resting  parts  of  the 
bod)-. 

When  the  bod)'  is  at  rest,  the  vessels  in  the  abdomen  and 
the  thorax  contain  more  than  one-half  of  all  the  blood. 
During  digestion,  the  quantity  of  blood  in  the  intestine  is 
larger  than  during  fasting.  During  work,  the  blood  vessels 
of  the  muscles  are  better  filled  with  blood  than  during  rest, 
simultaneously  the  abdominal  vessels  innervated  by  the 
splanchnic  are  constricted. 

In  the  suprarenal  glands  a  substance  is  formed  which  increases 
the  tonus  of  the  muscles  of  the  vessels.  It  acts  directly  upon  the 
muscle  fibres  (see  Chapter  XI). 

Small  losses  of  blood  are  compensated  by  general  con- 
striction of  the  vessels.  But  for  great  loss  of  blood,  amount- 
ing to  over  one-half  of  all  the  blood,  this  compensation  is 
not  sufficient;  the  blood  pressure  sinks  much,  the  valves  do 
not  close  completely  and  the  circulation  ceases.  Death  by 
loss  of  blood  in  such  cases  does  not  take  place  because  of 
lack  of  any  constituent  of  the  blood,  e.g.  the  haemoglobin, 
but  because  the  vessels  are  not  sufficiently  filled  and  this 
entails  disturbances  in  the  circulation.  If  the  lost  blood  is 
replaced  by  an  indifferent  fluid  {o.gf0  NaCl),  the  circulation 
is  resumed,  [transfusion].  If  the  loss  of  blood  amounts  to 
more  than  two-thirds  of  all  the  blood,  the  haemoglobin 
present  is  not  sufficient  for  respiration,  and,  notwithstanding 
that  the  circulation  may  be  repaired,  death  takes  place 
because  of  lack  of  oxygen.  In  such  a  case,  life  can  be  saved 
only  by  the  transfusion  of  human  blood.  Blood  from  other 
animals  cannot  be  used  because  of  "lobucidal  action. 


CHAPTER    V 

RESPIRATORY    MOVEMENTS 

THE  object  of  the  respiratory  movements  is,  by  alternately 
increasing  and  decreasing  the  thoracic  cavity,  to  suck  the  air 
into  the  alveoli  of  the  lungs,  and  after  gas-exchange  with 
the  pulmonary  blood,  to  force  it  out  again. 

1.  THE    CHANGE    IN  THE    FORM   OF   THE    THORACIC 
CAVITY    AND    OF   THE    LUNGS 

The  respiratory  movements  consist  of  the  alternate  increase 
(inspiration)  and  decrease  (expiration)  of  the  thoracic  cavity 
in  all  directions. 

i .  The  dilation  of  the  thoracic  cavity  in  the  perpendicular 
diameter  is  produced  by  the  contraction  of  the  diaphragm, 
which  descends  by  the  flattening  of  its  convexity.  In  this 
process  the  muscular  portions  play  the  most  important  part ; 
the  central  tendon  is  of  secondary  importance.  The  per- 
ipheral parts  of  the  diaphragm,  which,  in  expiration,  lie 
against  the  thoracic  walls,  are  during  inspiration  drawn 
away  from  the  walls.  In  expiration  the  intestine  forces  the 
diaphragm  upward  into  the  thoracic  cavity. 

2.  The  dilation  of  the  thoracic  cavity  in  the  horizontal 
diameter  is  brought  about  by  the  elevation  of  the  ribs. 

Each  rib  is  movably  joined  to  the  spinal  column  at  two  places: 

1.  By  its  head  to  two  vertebrae. 

2.  By  its  tubercle  to  the  transverse  process  of  one  vertebra. 
The  axis  about  which  the  rib  turns  passes  through  its  neck,  hence 
passes  in  almost  a  horizontal  anterior-posterior  direction. 

The  ribs  incline  forward  and  downward.  By  their  elevating  the 
degree  of  this  inclination  is  lessened.      By  this  means  the  cross- 

79 


So 


HUMAN   PHYSIOLOGY 


section  of  the  thoracic  cavity  is  increased  both  in  its  anterior- 
posterior  and  lateral  diameter,  as  the  horizontal  distance  between 
the  anterior  ends  of  the  ribs  and  the  spinal  column  increases  and 
the  lateral  parts  of  the  ribs  move  apart.  Simultaneously  with  the 
ribs,  the  sternum  is  raised  and  moved  forward.  The  elevating  of 
the  ribs  and  sternum  is  dependent  upon  the  twisting  of  the 
cartilage  of  the  ribs.  This  increases  the  obtuse  angle  (facing 
upward)  formed  by  the  cartilages  of  the  ribs. 

The  elevating  of  the  ribs  in  quiet  breathing  is  brought 
about  by  the  external  intercostal  and  the  intercartilaginous 
portion  of  the  internal  intercostals. 

The  fibres  of  the  external  intercostals,  placed  between  the  ribs, 
slant  forward  and  downward.  As  the  ribs  are  raised,  the  insertion 
points  of  any  fibre  approach  each  other,  hence  the  contraction  of 
the  muscle  fibres  elevates  the  ribs. 

The  intercartilaginous  portion  of  the  internal  intercostals  slants 
downward  and  backward  between  two  costal  cartilages  which 
slant  in  the  same  direction  as  the  muscles.      Here  also  the  points 


II.    B 


Fig.  2. 

of  insertion  approach  each  other  when  the  cartilages  are  raised. 
But  these  intercartilaginous  muscles  are  of  importance  only  in  the 
lower  costal  cartilages. 

In  the  above  scheme  (Fig.  2)  If  represents  the  spinal  column; 
B,  the  sternum ;  Rx  and  Ru  represent  two  ribs  with  their  external 
intercostal  muscle,  mr\  A\  and  A'u  are  two  cartilages  with  their 


RESPIRATORY  MOVEMENTS  81 

intercartilaginous  muscles,  mk.  In  I  the  position  in  expiration  is 
represented;  in  II,  that  in  inspiration.  It  is  evident  that  in 
II  mr  and  mk  are  shorter  than  in  I. 

In  forced  inspiration  the  following  muscles  aid  in  elevating  the 
ribs:  scaleni,  levatores  costarum,  serratus  posticus  superior, 
sterno-cleido-mastoid ;  also,  after  fixation  of  the  arm,  as  by 
gripping  the  table,  the  pectoralis  major  and  minor  and  serratus 
anticus  major.  During  forced  inspiration,  the  levatores  alae  nasi 
contract,  causing  dilation  of  the  nostrils,  and  also  the  crico-arv- 
tenoideus  postici  which  cause  the  dilation  of  the  vocal  bands. 

The  lowering  of  the  ribs  during  expiration  is  brought 
about  by  the  sternum  sinking  by  gravity  and  by  the  contrac- 
tion of  the  internal  intercostal  muscles.  These  muscles 
cross  the  externals  and  therefore  act  in  the  opposite  direc- 
tion. 

In  forced  expiration  the  ribs  are  lowered  by  the  serratus  posticus 
inferior  and  latissimus  dorsi ;  further  the  upward  movement  of  the 
diaphragm  is  aided  by  the  muscles  of  the  abdominal  Avails  and  the 
quadratus  lumborum,  which  also  aids  in  the  lowering  of  the  ribs. 

In  the  male,  the  respiration  is  chiefly  effected  by  the  lower 
parts  of  the  thorax,  in  the  female  by  the  upper. 

Normally,  the  intra-abdominal  pressure  sinks  slightly 
during  inspiration  and  rises  during  expiration.  Only  when 
the  intestines  are  abnormally  filled  with  food,  fasces  and 
gases,  does  the  intra-abdominal  pressure  rise  during  inspira- 
tion and  sink  during  expiration. 

The  lungs  are  two  sacs  with  extensible  and  elastic  walls, 
placed  hermetically  in  the  thoracic  cavity,  so  that  their 
external  surface  (pleura  pulmonalis)  is  everywhere  in  close 
contact  with  the  inner  surface  of  the  thoracic  wall  (pleura 
costalis),  but  the  two  pleura  are  not  grown  together.  The 
inner  surface  of  the  lungs  is  much  increased  by  thin  mem- 
branous projections  which  form  the  walls  of  the  alveoli. 
The  internal  space  of  the  lungs  communicates  with  the  at- 
mosphere by  means  of  air-passages  (bronchi,  trachea,  phar- 
ynx, nose).  The  atmospheric  pressure,  therefore,  presses 
upon  the  inner  surface  of  the  lung  and  keeps  the  external 
surface  of  the  extensible  lung-wall  against  the  thoracic  wall. 


82  HUMAN  PHYSIOLOGY 

After   expansion    of  the    thorax    the    atmospheric    pressure 
stretches  the  lung-sac  and  enlarges  it. 

Even  in  the  expiratory  position  of  the  thorax,  the  walls 
of  the  lungs  are  stretched.  If,  in  a  dead  body,  the  thoracic 
wall  is  opened  so  that  the  air  can  enter  the  pleural  cavity, 
the  lungs  withdraw  from  the  thoracic  walls.  If,  previous  to 
opening  the  thorax,  a  manometer  is  connected  with  the 
trachea,  this  will,  on  opening  the  thorax,  indicate  the 
pressure  which  the  tension  of  the  pulmonary  wall  exerts. 
In  the  pleural  cavity,  in  the  expiratory  position,  there  is  a 
corresponding  negative  pressure  of  about  3-5  mm  Hg. 
During  ordinal-}'  inspiration  this  is  increased  by  about  9  mm  ;, 
during  forced  inspiration,  by  30-40  mm. 

2.  THE  VARIATION  IX  PRESSURE  OF  PULMONARY 
AIR  DURING  RESPIRATION  ;  RESPIRATORY  CA- 
PACITY 

During  the  inspiratory  dilation,  the  pressure  of  the  air  in 
the  lungs  sinks,  while  during  expiration  it  rises.  This 
decrease  in  pressure  causes  the  external  air  to  rush  in ;  the 
increase  in  pressure  during  expiration  forces  the  air  out  of 
the  lungs.  These  respiratory  changes  in  pressure  amount, 
in  quiet  breathing,  to  1-3  mm  Hg;  in  forced  respiration 
they  are  greater. 

The  respiratory  volume  is  determined  by  exhaling  into  an  instru- 
ment used  for  measuring  the  volume  of  gases  (gasometer,  spirom- 
eter) or  by  letting  the  inhaled  or  exhaled  air  pass  through  a 
gas-meter. 

A  part  of  the  inspired  air  does  no  service  in  the  gas-exchange, 
as  it  does  not  reach  the  alveoli  but  remains  in  the  air-passage 
(trachea,  bronchi,  nose).  The  size  of  this  "dead  space"  is 
100-150  cc. 

Tidal  air  is  the  air  inhaled  and  exhaled  during  quiet 
respiration;   in  the  adult  male  it  is  about  500  cc. 

Complemental  air  is  the  air  which  can  be  inhaled,  in 
excess  of  the  tidal  air,  by  forced  inspiration ;  it  is  about 
2500  cc. 

Supplemental  air  is  the  air  which  can  be  expelled,  besides. 


RESPIRATORY  MOVEMENTS  83 

the  tidal  air,  by  the  most  forcible  expiration ;  it  is  about 
1500  cc. 

These  volumes  combined  form  the  vital  capacity  (4500  cc), 
i.e.  the  greatest  possible  inhaled  and  exhaled  volume  of  air. 

Residual  air  is  the  air  which,  after  the  deepest  expiration, 
remains  in  the  lungs  and  may  amount  to  about  1200  cc. 

Because  of  the  radiation  of  heat  and  the  evaporation  of 
water  from  the  mucous  membranes,  the  inspired  air  in  its 
passage  to  the  lungs  is  warmed  to  the  body  temperature  and 
saturated  with  water  vapor. 

Dust  which  has  been  brought  to  the  air-passages  by  inspiration 
is  forced  out  by  the  movement  of  the  cilia  of  the  epithelial  cells 
of  mucous  membrane. 

Respiratory  sounds.  During  breathing  the  movement  of  the 
air  produces  sounds- which  may  be  heard  by  placing  the  ear  upon 
the  chest-wall.  Above  the  trachea  and  the  bronchi  there  is  heard 
a  blowing  noise,  like  the  sound  of  the  German  "  ch  "  (bronchial 
breathing),  both  during  inspiration  and  expiration.  Above  the 
tissue  of  the  lungs  we  hear  a  sighing  sound  (vesicular  murmur) 
which  is  strong  during  inspiration,  feeble  during  expiration. 


3.  FREQUENCY  AND  RHYTHM  OF  RESPIRATORY 
MOVEMENTS.  INNERVATION  OF  THE  MUSCLES 
OF    RESPIRATION 

Adults  breathe  about  18  times  in  one  minute,  children 
oftener  (during  the  first  year,  on  the  average,  44  times). 

Expiration  follows  immediately  upon  inspiration.  The 
proportion  of  the  length  of  the  inspiration  to  that  of  expira- 
tion is  about  as  10  :  12.  Between  the  end  of  expiration  and 
the  beginning  of  the  next  inspiration  there  is,  as  a  rule  no 
pause. 

The  motor  nerves  for  the  muscles  of  respiration  proceed 
from  the  spinal  cord  at  the  anterior  roots  of  the  cervical  and 
dorsal  region.  They  are  the  phrenic  nerves  for  the  dia- 
phragm and  the  intercostal  nerves  for  the  intercostal  muscles. 

The  respiratory  centre  lies  in  the  medulla  oblongata,  on 
both   sides    of  the    posterior   point  of  the   fovea    rhomboid. 


84  HUMAN  PHYSIOLOGY 

Destruction    of   this   spot   causes    immediate    death    because 
breathing  stops  (hence  the  spot  is  called  the  nceud  vital). 

Some  authors  suppose  that  this  spot  is  a  nerve  trunk  which 
unites  the  nuclei  of  the  5,  9,  10  and  11  cranial  nerves  with  the 
nuclei  of  the  motor  respiratory  nerves.  It  has  also  been  advanced 
that  the  real  respiratory  centre  lies  not  in  the  medulla  but  in  the 
spinal  cord. 

The  centre  is  composed  of  an  inspirator)'  and  an  expiratory 
centre  which  act  alternately;  it  is  bilaterally  double,  but  the 
two  parts  are  connected  by  commissural  fibres  so  that  they 
are  always  stimulated  simultaneously. 

The  nerves  from  the  respiratory  centre  to  the  motor  nuclei 
of  the  nerves  of  respiration  run  in  the  two  lateral  columns  of 
the  spinal  cord  {respiratory  bundle). 

The  stimulation  of  the  respiratory  centre  can  be  brought 
about  directly  and  indirectly. 

1.  Direct  stimulation. — Normally  the  respiratory  move- 
ments take  place  involuntarily  because  the  respiratory  centre 
is  continually  and  directly  stimulated.  The  normal  stimula- 
tion is  automatic,  not  reflex  for  the  centre  retains  its  activity 
after  all  the  centripetal  nerves  which  can  stimulate  it  have 
been  severed. 

The  normal  stimulation  is  the  lack  of  oxygen  and  the 
accumulation  of  carbon  dioxide  in  the  blood.  As  the  arterial 
blood  contains  so  little  oxygen  and  so  much  carbon  dioxide, 
the  centre  is  stimulated  even  by  the  arterial  blood.  This 
brings  about  the  normal  quiet  breathing  which  is  called 
eupneea. 

If  the  blood  is  well  aerated  by  deep  respiration,  so  that  it 
contains  much  oxygen  and  little  carbon  dioxide,  the  respira- 
tory centre  is  not  stimulated.  Hence,  breathing  is  suspended 
— apnoea. 

Apnoea  is,  indeed,  partly  due  to  a  stimulation,  by  the  expansion 
of  the  lungs,  of  centripetal  inhibiting  vagus  fibres  (see  below); 
for,  after  section  of  the  vagi,  it  is  more  difficult  to  produce  apnoea. 

The  embryo  in  uterus  is  in  apncea,  the  blood  of  the  mother 
causing  a  sufficient  gas-exchange  in  the  placenta.  If  the  circula- 
tion   of   the   umbilical   cord   (by  compression,  fur  example,  of  the 


RESPIRATORY  MOVEMENTS  85 

cord)  or  if  gas-exchange  in  the  placenta  (by  premature  rupture 
of  the  placenta)  is  prevented,  lack  of  oxygen  and  accumulation  of 
carbon  dioxide  in  the  blood  of  the  embryo  takes  place.  This  can 
bring  about  respiratory  movements  before  birth. 

If,  by  lack  of  aeration,  the  arterial  blood  becomes  poorer 
in  oxygen  and  richer  in  carbon  dioxide  than  the  normal 
blood,  respiration  is  increased,  the  inspirations  becoming 
deeper  and  more  frequent — dyspnoea.  Strong  continued 
dyspnoea  finally  produces  death  through  paralysis  of  the 
respiratory  centre — suffocation,  asphyxia. 

The  normal  stimulation  of  the  respiratory  centre  by  lack 
of  oxygen  and  accumulation  of  carbon  dioxide  serves  to 
regulate  the  intensity  of  the  respiratory  movements  accord- 
ing to  the  need  of  the  organism. 

In  the  active  muscle  there  are  supposed  to  be  formed  other 
products  besides  the  carbon  dioxide  which  stimulate  the  respiratory 
centre. 

Many  authors  suppose  that  the  carbon  dioxide  does  not  only 
stimulate  the  centre  directly  but  also  indirectly,  in  that  it  stimu- 
lates the  endings  of  the  centripetal  nerves  in  the  tissue  where  it 
is  formed,  and  these  in  turn  rerlexly  increase  the  respiration. 

Increase  of  temperature  augments  the  action  of  the 
respiratory  centre — heat  dyspnoea  (e.g.  in  fever). 

2.  Indirect  stimulation  of  the  respiratory  centre  is  pro- 
duced by  stimulations  carried  to  the  centre  by  nerves. 

(a)  From  the  cerebral  hemispheres,  psychical  influences 
can  modify  the  number,  depth,  and  rhythm  of  inspirations. 
On  the  one  hand,  we  can,  to  a  certain  extent,  voluntarily 
influence  respiration;  while,  on  the  other  hand,  respiration 
is  involuntarily  influenced  by  the  emotions  (fear,  anger, 
etc.). 

(#)  Reflex  modifications  of  respiration  are,  e.g.,  the  expul- 
sive expirations  which  are  called  sneezing  and  coughing  and 
are  produced  by  the  stimulation  of  the  sensory  nerves  of  the 
mucous  membrane  of  the  nose  (trigeminus)  and  of  the  larynx 
(superior  laryngeal).  Besides  these  respiration  is  reflexly 
influenced  by  a  large  number  of  other  sensory  stimuli. 


86  .        HUMAN   PHYSIOLOGY 

The  most  important  reflex  influence  upon  breathing  is 
brought  about  by  the  vagus.  Section  of  both  vagi  causes 
deeper  but  slower  inspiration,  so  that  the  total  quantity  of 
air  expired  during  a  long  period  of  time  is  not  altered. 
Stimulation  of  a  central  end  of  a  'cut  vagus  produces  no 
typical  alteration  in  respiration.  Sometimes  the  effect  is 
predominantly  inspirator}-,  sometimes  expiratory.  If  the 
lungs  of  an  animal  are  artificially  inflated,  an  expiratory 
movement  is  produced ;  by  artificial  expiration  (sucking  the 
air  out  of  the  lung)  an  inspiratory  movement  is  called  forth. 
It  is  therefore  supposed  that  the  vagus  supplies  the  lungs 
with  two  kinds  of  sensory  fibres,  of  which  the  one  stimulates 
expiration,  the  other  inspiration  (inspiratory  inhibiting  and 
expiratory  inhibiting).  Of  these  the  first  is  stimulated  by 
inflation  of  the  lung  during  inspiration,  the  second  by  the 
collapse  of  the  lung  during  expiration.  By  means  cf  this 
mechanism  the  inspirations  are  decreased  or  increased. 

This  action  of  the  vagus  seems  to  have  for  its  object  to 
prevent  the  overfatigue  of  the  muscles  of  respiration,  for  by 
shallow  breathing  the  muscles  are  less  exerted. 


CHAPTER   VI 

LYMPH,    LYMPH    GLANDS,    SPLEEN 

1.   THE    LYMPH 

FROM  the  blood  capillaries  there  continually  transudes  to 
the  tissues  a  fluid,  which,  as  tissue  fluid,  surrounds  the  cells 
and  carries  to  them  their  nourishment.  After  the  giving  off 
of  these  substances  and  the  taking  up  of  the  end-products  of 
metabolism,  the  tissue  fluid  goes  as  lymph  from  the  minute 
tissue  spaces  to  the  lymph  vessels,  then,  proceeding  through 
the  great  lymph  trunk  (thoracic  duct,  right  lymphatic  duct) 
empties  into  the  blood  vessels.  A  part  of  the  tissue  fluid 
also  passes  directly  through  the  capillary  walls  again  into 
the  blood. 

The  lymph  is  a  clear,  salty  fluid,  having  a  specific  gravity 
of  1.007— 1.043  which  coagulates  spontaneously  after  being 
shed.  It  contains,  as  the  cellular  element,  lymph  corpuscles 
identical  with  the  leucocytes  of  the  blood,  and  the  plasma  of 
the  lymph  contains  the  same  substances  as  the  plasma  of  the 
blood.  These  substances  are  about  in  the  same  proportions 
as  in  the  blood  plasma  except  the  proteid  substances,  the 
percentage  of  which  is  somewhat  smaller  in  the  lymph  than 
m  the  blood.  The  lymph  found  in  the  lymph  vessels  of  the 
intestine  during  digestion  contains  the  absorbed  fat  in  the 
form  of  a  fine  emulsion  and  therefore  has  a  milky  appear- 
ance ;   it  is  called  chyle. 

In  man,  the  quantity  of  lymph   flowing  from  the  thoracic  duct 
is  estimated  at  1  to  2  litre  per  day. 

Lymph  formation. — In  the  transudation  of  the  lymph  from 
the    blood     capillaries,    physical     processes — filtration     and 

37 


88  HUMAN  PHYSIOLOGY 

diffusion  through  the  walls  of  the  vessels — play  a  part.  It 
is  still  a  question  whether  the  physical  processes  alone  cause 
the  lymph  formation,  or  whether,  besides  them,  a  special 
activity  of  the  capillary  endothelium  aids  in  this  formation, 
whereby  the  lymph  is  secreted  into  the  tissues  (just  as  the 
gland  epithelium  secretes  the  gland  secretion). 

The  movement  of  lymph. — The  movement  of  the  lymph  is 
maintained  by  the  force  which  the  ever  following  lymph 
forming  in  the  tissues  exerts  upon  that  previously  formed. 
The  movement  is  aided  by  the  compression  of  lymph  vessels 
by  the  skeletal  muscles.  The  backward  movement  of  the 
lymph  is  prevented  by  the  valves.  Aspiration,  by  means 
of  the  negative  pressure  in  the  thorax,  also  aids  the  move- 
ment of  the  lymph. 

Many  animals  are  provided  with  lymph  hearts  which  aid  in  the 
circulation  of  the  lymph. 

The  serous  cavities  (pleural,  pericardial  and  peritoneal  cavities) 
may  be  regarded  as  very  large  lymph  spaces;  they  generally  con- 
tain small  quantities  of  serous  fluid,  corresponding  to  the  lymph 
in  composition.  Soluble  substances  injected  into  these  serous 
cavities  are  absorbed  from  the  cavities  partly  by  the  blood  capil- 
laries, partly  by  the  lymph  vessels.  Concerning  the  force  which 
causes  this  absorption,  the  opinions  of  authors  differ.  But  it  is 
certain  that  this  absorption  is  aided  by  respiration.  By  means  of 
the  alternate  dilation  and  constriction  of  the  lymph  spaces  of  the 
diaphragm  and  pleura,  the  lymph  is  now  sucked  from  the  serous 
cavities  into  the  lymph  spaces  and  now  forced  from  the  lymph 
spaces  into  the  lymph  vessels.  Also  finely  divided  solid  substances 
(e.g.  fat,  pigments)  can  be  absorbed  from  the  serous  cavities  by 
the  lymph  vessels. 

2.   THE    LYMPH    GLANDS 

These  are  composed  of  reticular  connective  tissue  in 
whose  meshes  are  found  groups  of  cells.  Here  the  leucocytes 
originate  and  are  passed  into  the  lymph  which  enters  the 
meshes  by  the  afferent  vessel  and  leaves  by  the  efferent 
vessel. 

The  lymph  glands  also  filter  the  lymph  and  retain  worn- 
out   lymph   cells,   aLo   injurious   substances,   e.g.    Bacteria, 


L  YMPH,  L  YMPH   GLANDS,  SPLEEN  89 

which  enter  the  gland  with  the  lymph.     This  prevents  these 
substances  from  entering  the  general  circulation. 

The  retiform  tissue  through  which  lymph  passes  and  which 
serves  for  the  formation  of  leucocytes  is  also  found  in  certain 
other  bodies,  e.g.  in  many  parts  of  the  mucous  membrane  (solitary 
glands,  Peyer^s patches  of  the  intestine). 

The  thymus  gland  has  the  same  structure  and  function  as  the 
lymph  glands.  It  is  well  developed  in  the  embryo  and  child,  but 
begins  to  degenerate  at  the  tenth  year  and  finally  disappears 
entirely. 

3.   THE    SPLEEN 

The  spleen  consists  of  a  framework  which  is  made  of  a 
trabecular  tissue  and  supports  the  spleen-pulp,  a  reticular 
tissue  with  many  cellular  elements.  In  many  places  the 
cells  are  clustered,  forming  the  spleen  follicles.  Some  of 
the  cells  of  the  pulp  are  leucocytes,  some  are  large  multi- 
nuclear  cells,  some  are  red  blood  corpuscles  and  some  are 
cells  which  have  ingested  red  blood  corpuscles.  According 
to  most  authorities,  the  blood  is  supposed  to  flow  from  the 
capillaries  into  the  meshes  of  the  pulp  and  from  there  through 
the  splenic  vein. 

In  the  capsule  of  the  spleen  there  are  smooth  muscle  fibres 
which  by  their  contraction  regulate  the  size  of  the  spleen. 

Leucocytes  are  formed  in  the  spleen  and  thrown  into  the 
blood,  for  the  blood  in  the  splenic  vein  contains  more 
leucocytes  than  the  arterial  blood.  This  function  corre- 
sponds to  the  anatomical  structure  of  the  spleen,  which  is 
very  much  similar  to  that  of  lymph  glands.  But  white  blood 
corpuscles  are  not  only  formed  in  the  spleen  as  in  the  lymph 
glands,  but  they  are  also  destroyed  there.  This  is  supported 
by  the  fact  that  we  find  in  the  spleen  considerable  quantities 
of  substances  which  have  been  derived  lrom  the  nuclei  of  the 
destroyed  white  blood  corpuscles.  They  are  the  xanthin 
bases,  decomposition  products  of  nuclein,  which  must  be 
regarded  as  the  precursors  of  uric  acid.  If  the  spleen-pulp 
is  heated  with  blood,  uric  acid  is  formed.  As  it  is  supposed 
that,  in   mammals,  uric   acid  is  formed  from  the  nucleins   of 


9°  HUMAN   PHYSIOLOGY 

the  nuclei,  the  spleen  must  be  the  chief  place  of  uric  acid 
formation. 

The  fact  that  we  find,  in  the  spleen-pulp,  cells  which  con- 
tain red  blood  corpuscles,  in  all  stages  of  decay,  favors  the 
view  that  the  red  blood  corpuscles  are  also  destroyed  in  the 
spleen.  Red  blood  corpuscles  are  supposed  to  be  formed 
in  the  embryonic  spleen. 

The  spleen  can  be  extirpated  without  injury  to  the  body ; 
its  functions  can  be  entirely  taken  up  by  other  organs  (lymph 
glands,  red  bone  marrow,  liver). 

In  many  cases  of  infectious  diseases,  the  spleen  is  much 
enlarged.  Some  claim  that  the  spleen  produces  cells 
[phagocytes  ?]  which  neutralize  the  cause  of  the  disease. 


CHAPTER    VII 
SECRETIONS 

1.   SECRETIONS    IN    GENERAL 

SECRETIONS  are  of  various  significance  for  the  animal 
■economy.  Some  serve  to  remove  from  the  body  the  waste 
products  of  metabolism  (e.g.  secretion  of  urine) ;'  some  furnish 
the  fluids  necessary  for  the  digestion. and  absorption  of  foods  ; 
again,  there  are  the  secretions  of  milk-glands,  the  food  for 
the  infant;  the  secretion  of  the  sebaceous  glands,  a  protec- 
tive covering  for  the  skin ;  and  the  sweat  secretions  which 
regulate  the  temperature  of  the  organism. 

Secretions  are  produced  by  the  gland-cells,  i.e.  by  modi- 
fied epithelial  cells.      They  are  found: 

(a)   As  isolated  cells  between  other  epithelial  cells. 

In  this  group  belong  the  secreting  epithelial  cells  of  the  mucous 
membrane  (globlet  cells),  cylindrical  cells  which,  when  empty  of 
secretion,  contain  granular  protoplasm  and  oval  nuclei;  this 
granular  protoplasm  during  the  formation  of  secretions  changes  to 
a  clear  mass,  the  unchanged  protoplasm  and  the  nuclei  withdraw- 
ing to  the  bottom  of  the  cell.  The  clear  mass  then  leaves  the 
cell,  is  deposited  on  the  free  surface  and  constitutes  the  secretion. 
In  the  globlet  cells  the  formation  and  the  pouring  out  of  the 
secretion  take  place  simultaneously;  finally  the  whole  cell  empties 
itself  and  dies. 

(/?)   As  congregated  in  the  glands. 

The  glands  are  invaginations  of  the  skin  or  mucous  mem- 
brane of  various  forms,  some  in  the  form  of  tubes  (tubular), 
some  in  the  form  of  sacs  (acinous),  branched  or  unbranched. 

The  wall  of  the  gland  duct  forms  a  layer  of  cells  which  is 
supported  by  a  membrana  propria  and  surrounded  by  capil- 

91 


92  HUMAN  PHYSIOLOGY 

laries.  The  glands  also  contain  lymph  vessels,  muscles  and 
nerves. 

The  secreting  cells  are  generally  only  found  at  the  closed 
end  of  the  gland  duct,  while  the  other  part  serves  as  an 
excretory  duct  for  the  secretion. 

The  process  of  secretion  is  not  merely  a  filtration  of  the 
fluids  of  the  blood  through  the  walls  of  the  gland,  but  is 
brought  about  by  a  special  activity  of  the  secreting  gland- 
cell,  as  the  following  shows: 

i .  Most  of  the  secretions  contain  substances  not  found  as 
such  in  the  blood,  which  must  therefore  have  been  made  by 
chemical  processes  in  the  gland-cells  (e.g.  the  ferments  of 
digestive  fluids,    the  caseinogen  and  the  lactose  of  milk,  etc.). 

2.  Secretion,  in  many  cases,  does  not  occur  continually 
but  only  at  stated  times,  while  blood  pressure  should  cause 
a  continual  filtration. 

3.  The  pressure  of  the  secretion  in  the  duct  of  the  gland 
maybe  higher  than  that  of  the  blood.  Furthermore,  secre- 
tion can  take  place  in  glands  free  from  blood  and  even  in 
excised  glands. 

4.  In  many  cases  the  secretion  is  accompanied  by  morpho- 
logical changes  in  the  cells  of  the  gland. 

5.  Many  secretions  are  under  the  influence  of  specific 
secretory  nerves.  The  nerve-fibres  in  the  salivary  glands 
end  in  the  gland-cells. 

2.   SALIVARY    SECRETION 

1.  Composition  of  saliva. — The  saliva  of  the  mouth  is  a 
secretion  of  all  the  glands  of  the  mouth-cavity.  It  is  a 
colorless,  cloud}-,  string}-  fluid,  having  a  weak  alkaline 
reaction.  The  amount  secreted  in  twenty-four  hours  is 
estimated  at  from  one  to  two  litres. 

The  cloudiness  of  the  saliva  is  due  to  the  mucin,  salivary 
corpuscles  and  discarded  epithelial  cells  of  the  mouth-cavity. 
The  salivary  corpuscles  are  recently  loosened  gland-cells 
or  migrated  leucocytes. 

The  saliva  contains  99-99.5$  water,  0.1-0.2$  salts  (in- 


SECRETIONS 


93 


eluding  potassium  sulphocyanate),  o.  [-0.4$  organic  material 
including  proteids,  mucin  and  a  diastatic  ferment,  ptyalin, 
and  last  of  all,  gases,  especially  carbon  dioxide. 

2.  Morphological  phenomena  accompanying  salivary  secre- 
tion. -^-The  buccal  cavity  contains  two  kinds  of  glands: 

(a)  Albuminous  or  serous  glands  furnish-  a  secretion  free 
of  mucin.  To  this  class  belong  the  parotid  and,  in  many 
animals  (rabbits;,  the  submaxillary  also,  and  a  part  of  the 
glands  of  the  mucous  layer  of  the  mouth-cavity. 

The  cells  of  the  albuminous  glands  have,  during  rest,  a 
small  amount  of  clear,  finely  granular  protoplasm  and  a 
small  irregular  nucleus.  In  the  active  condition  the  cells  are 
smaller,  the  amount  of  the  granular  substance  is  increased, 
and  the  nuclei  become  more  nearly  spherical. 

(/?)   The    mucous    glands    furnish    a    secretion    containing 

81     a7       .  a,    a, 

/ 


b2L    ill 


Fig.  3. — Representing  the  Origin  of  Demilunes.     (After  Stohr.) 

mucin ;  this  group  contains  all  the  glands  except  the  albumi- 
nous glands. 

Many  glands,  e.g.  the  sub-maxillary  glands  of  man,  con- 
tain both  albuminous  and  mucous  gland-cells. 

In  the  mucous  glands  we  find  two  kinds  of  cells  : 

1.    The  demilune  of  Giannuzi    (also  called  border  cells) 


94  HUMAN  PHYSIOLOGY 

lying  at  the  periphery  of  the  gland  wall.     They  are  flattened 
cells  with  protoplasm  rich  in  granules. 

2.  Muciparous  cells,  reaching  to  the  lumen  of  the  gland 
duct;  their  protoplasm  is  but  slightly  granular,  more  hyaline. 

These  two  forms  of  cells  are  of  the  same  kind,  but  are  in 
different  conditions  of  secretion.  The  well-filled  muciparous 
cells,  a.  ,  a2,  a.,  (Fig.  3,  I)  crowd  the  empty  border  cells 
b  ,  b.t,  b„,  away  from  the  lumen.  After  discharging  their 
secretion,  the  hitherto  muciparous  cells  are  crowded  away 
by  the  now  filled  border  cells  and  are  themselves  changed 
to  border  cells  (compare  the  change  in  the  form  of  the  cells 
in  the  successive  stages  II,  III,  IV  of  Fig.  3). 

3.  Influence  of  the  nervous  system  upon  secretion. — The 
salivary  secretion  is  stimulated  reflexly  when  food,  especially 
dry  food,  stimulates  the  nerves  of  the  mucous  membrane  of 
the  mouth.  Salivary  secretion  is,  therefore,  dependent  upon 
the  nervous  system. 

The  submaxillary  and  sublingual  glands  are  supplied 
with  the  following  secretory  nerves: 

(«)  Fibres  from  the  facial  nerve  which,  passing  through 
the  chorda  tympani,  approach  the  glands  along  with  the 
lingual.  Stimulation  of  these  fibres  produces  a  rich  flow  of 
thin  secretion. 

(/;)  Fibres  from  the  cervical  sympathetic;  the  stimulation 
of  these  yields  a  scanty  flow  of  thick  saliva. 

The  chorda  fibres  also  contain  the  vaso-dilators ;  the 
sympathetic  contain  the  vaso-constrictors  for  the  blood 
vessels  of  the  glands. 

The  parotid  glands  are  supplied  with  the  following  secre- 
tory fibres : 

(a)  Fibres  from  the  glossopharyngeal  passing  through  the 
nervus  Jacobsonii,  Petrosus  superficialis  minor  to  the  oticum 
ganglion,  from  there  through  the  auricula  temporalis  to  the 
gland.  Stimulation  of  these  produces  a  great  (low  of  thin 
saliva. 

(It)  Fibres  of  the  cervical  sympathetic,  stimulation  of  which 
yields  a  scanty  flow  of  thick  secretion. 


SECRETIONS  95 

The  centre  of  the  secretory  nerves  is  situated  in  the 
medulla  oblongata. 

For  some  time  after  the  section  of  the  secretory  nerves  the 
gland  secretes  continuously  (paralytic  secretion)  till  it  finally  dies 
and  degenerates.  The  cause  of  this  paralytic  secretion  is  still  in 
the  dark. 

The  pressure  of  the  secretion  is  measured  by  placing  a  canula 
in  the  duct  of  the  gland  and  connecting  this  with  a  manometer. 
In  the  submaxillary  of  the  dog  the  pressure  during  chorda  stimula- 
tion may  be  above  200  mm  Hg,  this  being  100  mm  more  than  the 
blood  pressure  in  the  blood  vessels  of  the  gland. 

The  secretion  of  the  salivary  glands  is  said  to  be  warmer  than 
that  of  the  blood  carried  to  the  gland.  Hence  heat  is  produced 
during  salivary  secretion. 

The  active  gland  shows  certain  electrical  phenomena,  the  mean- 
ing of  which  is  not  yet  understood. 

* 

Upon  nervous  stimulation,  secretion  can  go  on  in  a  bled 

animal,  in  which  case  the  gland  is  no  longer  supplied  with 
blood. 

3.    GASTRIC    SECRETION 

1.  Composition  of  gastric  juice- — Gastric  juice,  the  secre- 
tion of  the  gastric  glands,  is  a  clear,  transparent  or  slightly 
yellowish  fluid >  having  an  acid  reaction  and  a  specific  gravity 
of  1.003— 1.006.  1^  contains  0.29-0.60$  solids  which  include 
o.  10-0.  \yf0  ash. 

Its  characteristic  constituents  are : 

(a)  Free  hydrochloric  acid,  in  man  o.  2$ ;  in  dogs  a  little 
more. 

The  gastric  juice  gives  the  following  tests  for  free  hydrochloric 
acid:  To  gastric  juice  add  Giinzburg's  reagent  (2  g  phloroglucin, 
1  g.  vanillin  in  30  g  absolute  alcohol)  and  evaporate.  This  gives 
a  red  color.  Gastric  juice  imparts  a  blue  color  to  methyl-violet 
and  congo-red. 

(b)  Pepsin,  a  ferment  which  in  an  acid  solution  digests 
proteids  and  gelatin.  According  to  its  composition,  it  is  a 
proteid-like  body.  The  antecedent  of  pepsin  in  the  gastric 
glands  is  the  pepsinogen,  a  substance  which  can  be  extracted 


96 


HUMAN   PH  YSIOL OG  Y 


from    the    gastric    glands   by  a    soda  solution,    and    can    be 
changed  to  pepsin  by  hydrochloric  acid. 

(V)  Rennin,  a  coagulating  ferment,  of  unknown  composi- 
tion. It  causes  the  casein  coagulation  of  milk.  Its  antecedent 
is  rennet-zymogen,  which  can  be  extracted  from  the  gastric 
mucosa  by  water  and  can  be  changed  to  rennin  by  the 
addition  of  acid. 

The  fasting  stomach  contains  no  gastric  juice  ;  its  mucous 
membrane  is  covered  with  mucus. 

2.  Morphological  phenomena  accom- 
panying the  secretion. — The  tubular 
glands  of  the  mucosa  may  be  classi- 
fied as : 

(a)  Glands  composed  of  only  one 
kind  of  gland-cell.  They  are  found 
in  the  pyloric  end  only  and  are  there- 
fore called  pyloric  glands. 

(/>)  Glands  composed  of  two  kinds 
of  cells ;  these  are  found  in  the  fundus 
— fundic  glands. 

The  pyloric  glands  contain  cylin- 
drical cells  which,  in  a  single  layer, 
form  the  duct.  The  fundic  glands 
contain,  besides  the  cylindrical  cells 
(the  so-called  chief  or  central  cells), 
also  a  second  kind  called  the  Ovoid  or 
oxyntic  cells.  These  ovoid  cells  lie 
isolated  between  the  chief  cells  and 
the  membrana  propria  and  do  not 
form  a  continuous  layer.  The  ovoid 
cells  are  surrounded  by  secretory  capil- 
lary loops  in  a  basket-like  form,  which  ovoid  cells  is  darker  and 
i         -4.1       . 1         i  r  j.1        granular.       Arrangement    of 

are   connected   with   the   lumen   of  the  fhe  ovoid  (a)  and &hief  ceUs 

""land.  (?')  °f  tne  fundic  glands. 

Both  the  fundic  and  pyloric  glands  form  pepsin  and  rennin, 
hence  the  cylindrical  cells  (chief  cells  of  the  fundic  glands)  must 
be  regarded  as  secreting  pepsin  and  rennin. 


Fig.  4.— Fundic  Glands. 
(After  Heidenhain.) 
The     protoplasm    of    the 
chief  cells  is  clear,  that  of  the 


SECRETIONS  97 

The  isolated  pyloric  end  of  the  stomach  secretes  a  gastric  juice 
-which  is  not  acid.  As  the  ovoid  cells  are  lacking  in  this  part,  it 
is  supposed  that  the  hydrochloric  acid  is  secreted  by  these  cells. 

The  morphological  changes  during  the  activity  of  the 
cells  are  as  follows:  The  chief  cells,  which  are  large  and 
granular  during  fasting,  at  first  become  still  larger,  but  from 
the  sixth  to  the  ninth  hour  of  digestion  theyr  become  smaller 
and  clearer.  The  ovoid  cells,  small  during  fasting,  are  much 
enlarged  during  digestion. 

Concerning  the  origin  of  the  characteristic  constituents  of 
gastric  juice,  nothing  is  known  for  certain.  Both  ferments  must, 
however,  be  regarded  as  a  product  of  the  gland-cells. 

As  to  the  formation  of  the  hydrochloric  acid  it  is  difficult  to 
understand  how  a  free  strong  acid  can  originate  while  the  blood 
and  the  secretory  cells  have  an  alkaline  reaction.  An  explanation 
has  been  sought  in  the  mass  action  of  weak  acids  (e.g.  carbonic 
acid)  upon  the  chlorides  of  the  blood.  In  the  same  way  as 
hydrochloric  acid  is  set  free  by  the  mass  action  of  the  carbonic 
acid  of  the  blood  upon  sodium  chloride  and  is  then  taken  up  by 
the  blood  corpuscles  (see  page  59),  the  mass  action  of  carbonic 
acid  in  the  ovoid  cells  might  set  free  the  hydrochloric  acid. 

Recently  it  has  been  supposed  that  the  acid  is  not  formed  in  the 
gland-cells,  but  is  formed  from  the  chlorides  of  the  food  in  the 
following  manner : 

By  dissolving  in  water  a  part  of  the  sodium  chloride  of  food  is 
split  up  into  sodium  and  chlorine  ions.  The  free  sodium  ions  in 
the  stomach  are  supposed  to  pass  through  the  walls  of  the  stomach 
by  diffusion  in  exchange  for  the  free  hydrogen  ions  of  the  blood. 
The  walls  of  the  stomach  are  impermeable  to  the  chlorine  ions, 
hence  they  remain  in  the  stomach  and  form,  with  the  hydrogen 
ions  coming  from  the  blood,  the  hydrochloric  acid.  This  view  is 
based  upon  the  following  facts:  (1)  The  cells  remain  alkaline 
notwithstanding  the  acid  formation;  (2)  If  chlorides  are  not 
present  in  the  stomach,  no  free  acid  is  supposed  to  be  formed; 
(3)  The  alkalinity  of  the  blood  and  of  the  urine  is  increased  after 
the  eating  of  sodium  chloride. 

3.    Influence  of  the  nervous  system  on  secretion. 

Observations  on  the  secretion  of  gastric  juice  can  be  easily  made 
on  men  and  animals  by  means  of  a  gastric  fistula. 

Gastric  secretion  begins  when  food  has  been  swallowed, 
even  when  food  passes  out  by  an  esophageal   fistula  so  that 


9$  HUMAN   PHYSIOLOGY 

it  does  not  reach  the  stomach.  This  secretion  stops  after 
the  cutting  of  the  vagi. 

The  secretion  is  dependent  upon  psychical  conditions,  as 
it  can  be  brought  about  by  the  mere  sight  of  food.  After 
section  of  the  vagi,  secretion  still  occurs  when  food  is  placed 
in  the  stomach  itself.  Whether  this  secretion  is  a  reflex 
process  in  which  the  vagus  does  not  participate,  or  whether 
it  is  due  to  direct  stimulation  of  the  glands,  is  not  known. 

The  secretion  of  the  gastric  juice  is,  therefore,  called  forth 
by  the  sight  and  deglutition  of  food  and  is  then  continued 
by  the  presence  of  the  food  in  the  stomach. 

4.    PANCREATIC    SECRETION 

I.  Composition  of  pancreatic  juice. — The  pancreatic  juice 
from  a  newly  placed  fistula  in  the  pancreatic  duct  is  a  clear, 
thick  fluid  having  a  specific  gravity  of  1. 03.  Because  of  its 
sodium  carbonate  (0.2^)  it  has  a  strong  alkaline  reaction. 
Sometimes  it  coagulates  spontaneously.  From  a  permanent 
fistula  the  secretion  is  not  so  thick  (sp.  gr.   1.01). 

The  pancreatic  juice  obtained  by  a  temporary  fistula  con- 
tains about  90^  water,  that  by  a  permanent  fistula  98$. 
The  solids  contain  from  0.6-0.9?©  ash,  also  organic  sub- 
stances, especially  proteids  (from  a  temporary  fistula  about 
10$).  The  secretion  from  a  temporary  fistula  is  frequently 
so  rich  in  proteids  that,  on  heating,  it  coagulates  to  a  solid 
mass.  Pancreatic  juice  also  contains  leucin,  fat,  soaps  in 
small  quantities,  and  the  following  three  characteristic 
ferments : 

{a)  A  diastatic  ferment,  which  acts  upon  starch  like  the 
ptyalin  of  saliva. 

(b)  Trypsin,  a  ferment  splitting  proteids  up  into  proteoses. 
Trypsinogen,  the  antecedent  of  trypsin,  is  changed  to  trypsin 
during  secretion  and  also  by  the  action  of  oxygen  or  organic 
acids. 

(c)  Steapsin,  a  fat-splitting  ferment,  which  splits  the 
neutral  fats  into  glycerin  and  fatty  acids. 


SECRETIONS  99 

2.   Morphological  phenomena  accompanying  the  secretion. 

. The  cells  of  the   pancreatic  glands  have  a  striated   outer 

and  granular  inner  zone.  During  activity  the  striated  outer 
zone  is  widened,  the  granular  inner  zone  decreases,  while 
during  rest  the  opposite   take    place   (see   Fig.    5).      In  the 


B 

Fig.  5. — Gland-cells  of  Pancreas  in  Difeerent  Stages  of   Secretion. 
(After  Heidenhain.) 
A,  first  stage  of  digestion  (6-10  hours);   the  striated  outer  zone  is  much  broader 
than  the  granular  inner  zone.      B,  second  stage  of  digestion  (10-20  hours);   the 
striated  outer  zone  is  narrower  and  the  inner  granular  zone  is  wider. 

active  condition  the  cells  are  separated  by  sharper  (frequently 
double)  boundary  lines  than  during  rest. 

3.  Influence  of  the  nervous  system  upon  secretion. — Secre- 
tory nerves  for  the  pancreas  are  supposed  to  be  present  in 
the  vagus  and  in  the  sympathetic. 

It  has  been  stated  that  the  pancreas  of  herbivorous 
animals  secretes  continuously,  while  that  of  carnivorous 
animals  secretes  periodically,  i.e.  only  after  the  introduction 
of  food  in  the  stomach. 

Among  the  substances  in  the  stomach  which  can  reflexly  cause 
pancreatic  secretion  are  chiefly  acids,  fats,  and  spices. 

Concerning  the  effects  of  extirpation  of  the  pancreas  see 
Chapter  XL 

5.   BILE    SECRETION 

1.  Composition  of  bile.  —  Bile,  the  secretion  of  the  liver, 
is  a  reddish-yellow  or  green  ropy  substance,  having  an 
intensely  bitter  taste.  When  it  is  poured  from  the  liver  it 
contains  about  1.5-3$  solids.  During  fasting  the  bile  does 
not  flow  directly  into  the  intestine,  but  first  into  the  gall- 
bladder, where  it  is  concentrated  by  the  absorption  of  water 
and  the  addition  of  mucus,  so  that  it  contains  about  16-17$ 


loo  HUM  Ah!  PHYSIOLOGY 

solids.  The  amount  secreted  per  diem  in  the  adult  is  about 
i  litre. 

Characteristic  constituents  of  bile  : 

(a)  Sodium  glycocholate  and  sodium  taurocholatc  (about 
one-third  of  all  the  solids  of  bile).  In  man  the  sodium 
glycocholate  predominates,  in  the  dog,  sodium  taurocholate. 

To  isolate  the  salts  of  the  bile  acids,  proceed  as  follows: 
Mix  bile  with  animal  charcoal,  evaporate,  extract  the 
residue  with  alcohol,  add  excess  of  ether;  this  precipitates 
the  salts  of  bile  acids  in  delicate  needle  crystals  (crystallized 
bile).  Concerning  the  characteristics  of  the  bile  acids  see 
page  49. 

if)  Bile  pigments,  bilirubin,  biliverdin,  and  sometimes 
also  hydro-bilirubin  ;   see  page  50. 

Besides  these,  bile  contains  mucin,  cholesterin,  lecithin, 
fat  and  fatty  acids,  salts  (chiefly  sodium  carbonate  and  phos- 
phate), and  a  little  iron. 

In  the  gall-bladder  the  solid  constituents  of  the  bile  may  be 
precipitated  as  gallstones.  These  may  be  composed  of  a  com- 
pound of  calcium  with  bilirubin  or  of  cholesterin. 

2.  Chemistry  of  the  liver. — The  liver  is  the  largest  gland 
in  our  body.  It  weighs  about  1.5  kg  and  contains  about 
30^  solids,  chiefly  proteids  (20$),  some  fats,  extractives,  and 
a  varying  amount  of  carbohydrate  in  the  form  of  glycogen 
and  grape-sugar.  Its  ash  forms  about  1$  of  its  weight  and 
is  characterized  by  its  high  per  cent  of  iron. 

The  iron  in  the  liver  is  partly  in  inorganic,  partly  in  organic 
combination.  The  iron  held  in  organic  union  is  found  in  two 
nucleo-proteids,  hepatin  and  ferratin.  In  the  hepatin  the  iron  is 
held  very  closely,  but  ferratin  lias  more  the  character  of  an  iron 
albuminate  since  its  iron  can  be  split  off  by  hydrochloric  acid. 

The  iron  of  the  liver,  like  the  bile  pigments,  is  derived  from  the 
haemoglobin  of  the  red  blood  corpuscles  which  are  destroyed  in 
the  liver.  The  iron  is  excreted  chiefly  by  the  walls  of  the  intes- 
tine, and  in  smaller  quantities  by  the  bile  and  urine. 

3.  Structure  of  the  liver. — The  gland-cells  of  the  liver  are 
irregular  polygonal  cells  having  granular  protoplasm  and 
one    or    more    nuclei.      The    protoplasm    contains    pigment 


SECRETIONS 


101 


granules  and  fat  droplets  and,  in  well-fed  animals,  masses 
of  glycogen.  In  the  fasting  condition  the  cells  are  small, 
cloudy,  and  have  not  well-defined  contours  ;  during  digestion 
they  are  larger,  the  centre  being  clear  and  the  periphery 
containing  large  granules. 

When  a  liver  is  cut  through,  the  liver  lobules  (Fig.  6)  can  be 
seen.     These  are  composed  of  cells  arranged  in  rows,  radiating 

from  a  vein  (the  vena  centralis)  in  the 
centre  of  the  lobules  to  the  circum- 
ference. Bat  these  rows  of  cells  are 
not  isolated,  for  each  cell  is  connected 
with  those  above  and  below  it. 

Between  the  cells  are  found  both 

the  small  bile  ducts  (the  so-called  bile 

capillaries)  and  the  blood  capillaries. 

The  bile  capillaries  stand  in  the  same 

relation  to  the  liver  cells  as  the  lumen 

of  other  cells  to  the  gland-cells.    Two 

Fig.    6.— Cross-section    of   a   cells  form  the  wall    of  the  bile  capil- 

Liver    Lobule    of    a    Pig.    lary,  the  latter  being  formed  by  two 

Radial    Arrangement    of   groove-like  depressions  in  the  surtaces 

the  Liver  Cells.  q£  twQ    neighboring   cells    which    are 

(After  Heidenhain.)  fiUed  together       Each  Uver  ce]1  comeS 

in  contact  with  bile  capillaries  on  more  than  one  side.  The  bile 
capillaries  empty  into  the  bile  ducts  coursing  between  the  lobules. 

The  blood  capillaries  originate  from  the  intralobular  branch  of 
the  portal  vein,  they  traverse  the  lobules  radially  and  finally  join 
the  central  vein  of  the  lobule  which  connects  with  the  intralobular 
branch  of  the  hepatic  vein.  The  blood  capillaries  also  run 
between  the  liver  cells,  but  in  such  a  manner  that  the  blood  and 
bile  capillaries  never  touch  each  other  but  are  surrounded  on  all 
sides  by  liver  cells.  Hence,  a  liver  cell  or  a  pari  of  a  liver  cell  is 
always  placed  be/ween  a  blood  and  a  bile  capillary. 

The  branches  of  the  hepatic  artery  run  only  in  the  intralobular 
tissue;  their  capillaries  empty  in  veins  which  end  in  the  portal 
vein.      The  lymph  vessels  accompany  the  portal  vein. 

4.    The  formation  of  bile. 

The  secretion  of  bile  can  be  investigated  by  means  of  the  biliary 
fistula. 

The  secretion  of  bile  is  continuous,  but  is  increased  3—5 

hours  after  the   taking   of  food.      This  increase  of  secretion 

during   digestion   seems    to   be   brought   about  by  absorbed 

substances  which  stimulate  the  liver  directlv.      As  such,  the 


102  HUMAN  PHYSIOLOGY 

bile  elements  (bile  acids;  absorbed  from  the  intestine  are 
especially  active. 

The  pressure  in  the  bile  ducts  may  be  higher  than  that  in 
the  portal  vein,  yet  the  secretion  of  bile  is  dependent  upon 
blood  pressure.  If  the  blood  pressure  decrease,  less  bile  is 
secreted  and  the  bile  contains  more  solids.  Ligaturing  the 
portal  vein,  stimulation  of  the  spinal  cord  and  of  the 
splanchnic  nerve  (because  of  diminished  amount  of  blood 
carried  to  the  liver,  due  to  the  constriction  of  the  arteries), 
cause  inhibition  of  bile  secretion. 

Secretory  nerves  for  the  liver  have  not  yet  been  demon- 
strated. 

5.    The  discharge  of  bile. 

The  bile  is  driven  out  of  the  liver  by  the  pressure  of  the  newly 
made  bile.  The  ductus  choledochus  has  at  its  opening  into  the 
intestine  a  sphincter  which  regulates  the  flow  of  the  bile.  The 
muscles  of  the  gall-bladder  and  ductus  choledochus  also  aid  in 
discharging  the  bile.  The  nerves  for  these  muscles  are  supposed 
to  be  the  vagus  and  splanchnic. 

If  the  flow  of  bile  is  prevented,  the  bile  enters  the  lymph  vessels 
and  thence  passes  into  the  blood  (jaundice).  The  bile  is  then 
excreted  by  the  kidneys. 

6.   SECRETION    OF    INTESTINAL   JUICE 

To  investigate  the  secretion  of  the  intestinal  glands,  an  intes- 
tinal fistula  must  be  made.  A  piece  of  the  intestine  is  isolated 
but  its  connection  with  the  mesentery  is  not  severed.  Either  both 
ends  of  this  piece  of  intestine  are  sewn  into  the  incision  of  the 
abdominal  wall,  or  only  one  end  is  thus  fixed  while  the  other  is 
closed  by  a  ligature.  The  two  ends  of  the  main  intestine  are  sewn 
together. 

1.  Composition  of  intestinal  juice. — The  juice  of  the  small 
intestine  is  a  colorless,  alkaline  fluid  having  a  specific  gravity 
of  i.OOJ.  It  contains  besides  salts,  some  proteids,  a  diastatic 
and  an  inverting  ferment,  and,  according  to  some  authors,  a 
proteolytic  ferment. 

The  large  intestine  furnishes  a  mucous  secretion  without 
ferments. 

2.  The  secretion. — The   intestinal  juice  is  the  secretion  of 


SECRETIONS  103 

the  glands  of  Brunner  in  the  duodenum  and  of  the  crypts  of 
Lieberkiihn  in  the  whole  intestine.  Concerning  the  secre- 
tion of  Brunner's  glands  and  the  conditions  of  their  secre- 
tion nothing  is  known. 

The  crypts  of  Lieberkiihn  of  the  small  intestine  are 
simple  tubular  glands,  placed  in  thick  clusters  between  the 
villi  of  the  mucous  membrane.  They  secrete  the  intestinal 
juice  containing  the  diastatic  ferment.  The  secretion  takes 
place  when  the  mucous  membrane  of  the  intestine  is  direct- 
or reflexly  stimulated  by  the  taking  up  of  food.  As  the 
secretion  also  takes  place  in  those  parts  of  the  intestine  not 
directly  stimulated,  it  is  dependent  upon  the  nervous  system. 
The  secretory  nerves  are,  however,  not  known. 

The  muciparous  glands  of  the  large  intestine  contain  many 
globlet  cells  forming  mucus;  these  globlet  cells  are  only 
found  occasionally  in  the  glands  of  the  small  intestine. 

The  intestinal  glands  also  seem  to  regenerate  the  epithelial 
glands  of  the  villi.  In  the  intestinal  glands  new  cells  are  con- 
tinually formed  by  mitotic  division;  these  new  cells  pass  upward 
to  take  the  place  of  the  broken-down  epithelial  cells  of  ihe  free 
surface  of  the  mucous  membrane. 

7.    RENAL    SECRETION 

1.  Composition  of  urine. — Urine,  the  secretion  of  the 
kidneys,  is,  in  man,  a  yellow  or  reddish-brown  fluid  having 
a  specific  gravity  of  1. 01 7- 1.040.  Its  reaction  is  generally 
acid  (due  to  acid  sodium  phosphate),  but  after  a  meal  of 
vegetables  containing  the  salts  of  vegetable  acids,  which  in 
the  body  form  carbonates,  it  may  be  neutral  or  alkaline. 
Its  reaction  is  alkaline  also  during  the  period  of  greatest 
gastric  digestion  because  the  alkalinitv  of  the  blood  is 
increased  on  account  of  the  acid  formation  in  the  stomach, 
and  this  excess  of  alkali  is  excreted  in  the  urine. 

When  urine  stands  for  a  certain  length  of  time,  putrefaction  sets 
in  by  which  the  urea  is  changed  to  ammonium  carbonate  (alkaline 
urea  fermentation)  ;  this  causes  the  urine  to  become  alkaline. 
Such  alkaline  urine  is  cloudy  because  of  a  precipitate  of  ammonio- 


104  HUM/IN  PHYSIOLOGY 

magnesium  phosphate,  ammonium  urate,  and  the  phosphates  and 
carbonates  of  the  alkali  earths. 

The  amount  of  urine  excreted  per  day  is  generally  about 
1.5  litres. 

Urine  contains  about  4$  solids,  among  which  are: 

(a)  Nitrogenous  wastes  of  metabolism:  urea  2.3$  (35  g. 
per  day),  uric  acid  (0.05$  in  the  form  of  acid  salts  of  the 
alkalies),  hippuric  acid,  kreatinin  (0.05$),  xanthin,  hypo- 
xanthin,  ammonia  salts  (0.04$).  The  urea  contains  83-86^ 
of  all  the  nitrogen  of  the  urine. 

To  obtain  the  urea  from  urine,  evaporate  the  urine  to  small 
bulk  and  add  nitric  acid ;  this  throws  down  crystals  of  nitrate  of 
urea. 

The  uric  acid  crystallizes  from  the  urine  when  that  is  mixed 
with  one-tenth  its  volume  of  concentrated  hydrochloric  acid  and 
left  standing  in  the  cold.  This  separation  of  the  uric  acid  takes 
place  in  concentrated  and  strongly  acid  urine  without  the  addition 
of  hydrochloric  acid  (sedimentum  lateritium,  see  page  46). 

The  urea  contains  83-86$  of  all  the  nitrogen  of  the  urine; 
ammonia  contains  3-4$  ;  the  remaining  nitrogen  is  distributed 
among  uric  acid,  kreatinin,  etc. 

(b)  Salts  about  1.5$,  chiefly  sodium  chloride  (a  little  more 
than  ifc)  and,  in  smaller  quantities,  phosphates,  sulphates, 
and  traces  of  oxalates;  among  the  bases  are  sodium,  potas- 
sium, magnesium,  calcium,  and  traces  of  iron. 

Besides  the  sulphates,  the  urine  contains  sulphuric  acid  combined 
with  the  ethereal  sulphates  of  the  benzene  derivatives,  e.g.  : 

Phenyl-sulphuric  acid Ct.H..O.SO,.OH 

Kresyl-sulphuric  acid C.H°.O.S02.OH 

Indoxyl-sulphuric  acid  or  indican C8HgN.O  SO.,. OH 

Skatoxyl-sulphuric  acid C9HgN.(  ).S(  )2.OH 

To  demonstrate  the  presence  of  indican,  add  a  like  quantity  of 
concentrated  hydrochloric  acid  and  a  little  calcium  chloride  solu- 
tion to  the  urine.  Indigo  is  produced  which  may  be  collected  by 
shaking  it  with  chloroform. 

The  benzene  derivatives,  with  which  the  sulphuric  acid  unites, 
are  derived  from  the  intestine,  where  they  are  formed  by  proteid 
putrefaction:    phenol,    indol,    skatol ;    the    last    two,    after    being 


SECRETIONS  105 

absorbed,  are  oxidized  to  indoxyl  and  skatoxyl.  From  this 
decomposition  of  the  proteid  in  the  intestine  arise  aromatic 
oxyacids  (oxyphenyl- acetic  acid  and  oxyphenyl-propionic  acid), 
which  are  absorbed  from  the  intestine  and  excreted  bv  the  kidnevs. 

(c)  In  small  quantities  there  are  present  in  the  urine 
urinary  pigments,  among  which  is  sometimes  found  urobilin, 
which  is  supposed  to  be  identical  with  hydro-bilirubin. 

Finally  there  are  present  in  urine,  gases,  chiefly  carbon 
dioxide,  traces  of  nitrogen  and  oxygen. 

In  certain  diseases,  e.g.  diabetes,  the  urine  contains- 
grape-sugar,  aceton,  oxybutyric  acid  and  diacetic  acid;  in 
inflammation  of  kidneys  it  contains  proteids ;  in  icterus,  bile 
pigments  and  acids;   and  in  hematuria,  blood  pigments. 

2.    The  structure  of  t lie  kidneys. 

The  kidneys  are  composed  of  a  uniformly  darkly  stained  cortex 
and  a  radially  striated  medulla  consisting  of  a  large  number  of 
Malpighian  pyramids. 

In  the  cortex  the  uriniferous  tubules  of  the  gland  are  coiled 
(convoluted  tubules);  in  the  medulla  they  are  straight  (tubuli 
recti).  Each  uriniferous  tubule  begins  in  the  cortex  (R,  Fig.  7) 
as  a  spherical  dilation,  the  Malpighian  body  (g),  from  which  pro- 
ceeds the  convoluted  tubule  (/").  This  proceeds  downward  into 
the  medulla,  M,  as  a  straight  tubule  (<?),  then  turns  and  forms  the 
loop  of  Henle.  The  ascending  limb  of  Henle's  loop  joins  the 
intercalated  part  (c),  which,  turning  downward  towards  the  pelvis, 
forms  a  straight  collecting  tubule  (J>).  The  collecting  tubules  join 
to  form  a  duct  (a),  which  at  the  apex  of  the  pyramids  empties  into 
the  pelvis  of  the  kidneys. 

The  Malpighian  bodies  are  composed  of  a  knot  of  blood  vessels, 
the  glomerulus  (g),  which  is  placed  in  the  blind,  sac-like  ending 
of  the  uniferous  tubule  (the  Bowman  capsule)  so  that  it  is  almost 
entirely  surrounded  by  the  capsule.  The  fold  of  the  capsule 
bordering  on  the  glomerulus  is  composed,  in  young  individuals, 
of  cuboidal  cells,  while  in  older  persons  the  cells  are  flattened. 
The  outer  fold  of  the  capsule  is  made  up  of  flat  polygonal  cells. 
It  is  continued  downward,  forming  the  walls  of  the  convoluted 
tubule  whose  cells  are  radially  striated  and  have  granular  proto- 
plasm. The  cells  in  the  walls  of  Henle*s  loop,  of  the  intercalated 
portion,  and  of  the  collective  tubules  are  cylindrical  epithelial  cells. 

The  uriniferous  tubules  are  surrounded  by  connective  tissue,  in 
which  are  found  the  blood  vessels. 

The  branches  of  the  renal  artery  proceed  from  the  hilus  to  the 
boundary  between  the  cortex  and  medulla  (a,  Fig.  8).      Here  they 


io6 


HUMAN   PHYSIOLOGY 


give  off  branches  which  radiate  outward  (6)  and  send  branches 
to  each  of  the  glomeruli  (c).  After  giving  off  these  branches, 
the  arterial  trunk  ends  in  capillaries  in  the  outer  part  of  the 
cortex  (d). 

Each  glomerulus  is  formed  by  the  afferent  vessel    (vas  afferens) 


Fig 


-Diagram  of  a  Urinary  Tubule. 


dividing  into  a  great  number  of  loops.  These  loops  then  join 
each  other  again,  forming  the  vas  efferens  (/)  which  passes  out  of 
the  glomerulus  and  then  splits  up  into  capillaries.  The  capillary 
net  in  the  cortex  surrounds  the  convoluted  tubules  (g). 

The  arteriolae  rectae  (/(')  in  the  medullary  portion  are  derived 
partly  from  the  rasa  afferentia  of  the  deepest  glomeruli,  partly 
from  the  renal  artery  directly.  These  form  straight  capillaries  in 
the  medulla,  and  at  the  papilla;  (?//)  form  a  ring-like  capillary  net- 
work.     The  capillaries  in  the  cortex  empty  into  the  veins  radiating 


SECRETIONS 


107 


^— 6 


-/ 


— k 


from  the  pelvis  to  the  circumference  (Ji);  into  these  the  smallest 
veins  of  the  medulla  also  empty  (/).  ^e 

3.    Conditions  of  renal  secretion. 

{a)  The  quantity  of  urine  secreted 
depends  upon  the  blood  pressure  in 
the  renal  artery;  it  decreases  when, 
e.g.  by  bleeding,  the  blood  pressure 
decreases;  it  increases  when,  e.g.  by 
ligaturing  of  other  blood  vessels,  the 
pressure  in  the  renal  arteries  is  in- 
creased. 

Partial  closure  of  the  renal  vein  (venous 
statis)  decreases  renal  secretion,  which 
appears  to  be  due  to  the  compression  of 
the  urinary  tubules  by  the  strongly  dilated 
capillaries  and  smaller  veins. 

(b)  The  renal  secretion  ceases  for 
a  long  time  when  the  supply  of  blood 
to  the  kidneys  has  been  cut  off  by 
compression  of  the  renal  artery  for 
but  a  few  minutes. 

(r)  There  are  certain  substances 
which,  taken  into  the  body,  increase 
renal  secretion,  e.g.  water,  urea,  so- 
dium chloride,  sodium  nitrate,  caffein, 
grape-sugar.  The  action  of  these 
diuretics  still  takes  place  when  the 
renal  secretion  has  been  entirely 
stopped  by  a  too  low  blood  pressure. 
On  the  other  hand,  there  are  sub- 
stances, e.g.  atropin,  which  inhibit 
renal  secretion. 

(d)   Concerning    the    effect   of   the 
nervous  system  upon    renal   secretion 
— leaving  out  of  consideration  the  in- 
direct influence   of  the   vaso-motor  nerves — nothing  is   yet 
known. 

Notwithstanding    the    fact   that    renal    secretion    depends 


-m 


FiCx.  8.  —  Scheme  ok  the 
Blood  Vessels  ok  Kid- 
neys. 


io8  HUMAN  PHYSIOLOGY 

upon  blood  pressure,  we  cannot  regard  it  as  a  mere  process 
of  filtration  of  the  blood  fluid  through  the  walls  of  the  urinary 
tubules.      This  assertion  is  based  upon  the  following  facts : 

1.  The  composition  of  the  urine  differs  quantitatively  from 
that  of  proteid-free  blood  plasma.  Main-  substances  (e.g. 
urea)  are  much  more  abundant  in  the  urine  than  in  blood. 

2.  The  harmful  effect  of  ligaturing  the  renal  artery  cannot 
be  explained  on  the  theory  of  mere  filtration. 

Renal  secretion  is,  therefore,  dependent  upon  the  special 
activity  of  the  gland-cells.  These  cells  are  temporarily 
paralyzed  by  the  stoppage  of  circulation  (compression  of 
renal  artery),  so  that  they  are  not  able  to  secrete.  Diuretics, 
in  so  far  as  they  do  not  affect  blood  pressure,  stimulate  the 
cells  toward  greater  activity. 

According  to  the  theory  accepted  at  present,  renal  secre- 
tion takes  place  as  follows:  The  cells  of  the  Bowman  capsule 
secrete  chiefly  water,  while  the  cells  of  the  convoluted  tubules 
secrete  the  solid  constituents  of  urine,  and  this  secretion  is 
concentrated  as  it  passes  through  the  urinary  tubule  by  the 
absorption  of  water  from  it. 

This  view  is  based  on  the  fact  that  sodium-sulphindigotate, 
injected  into  the  blood,  is  excreted  by  the  kidneys,  and  is 
found,  during  its  excretion,  only  in  the  inner  part  of  the  cells 
of  the  convoluted  tubules  and  lower  down  in  the  lumen  of 
the  urinary  tubules,  while  it  is  never  found  in  the  cells  of  the 
capsule. 

Most  of  the  substances  excreted  in  the  urine  are  not  formed 
in  the  kidneys  but  in  other  organs,  and  are  carried  by  the 
blood  to  the  kidneys  to  be  picked  out  by  them.  Some  sub- 
stances can  also  be  made  in  the  parenchyma  of  the  kidneys, 
e.g.  the  hippuric  acid.  That  energetic  oxidations  take  place 
in  the  kidneys  is  proven  by  the  facts  that  the  blood  in  the 
renal  veins  is  venous,  and  that  the  secreted  urine  is  often 
warmer  than  the  blood  flowing  to  the  kidneys. 

Beside  the  end-products  of  metabolism,  there  are  also 
excreted  substances  which  are  indeed  normal  constituents  of 
the   body  but  which,  for   some   reason,  have   accumulated  in 


SECRETIONS  109 

the  blood  in  too  large  quantities  (e.g.  many  salts,  grape- 
sugar  in  case  of  glycosuria),  also  substances  normally  not 
found  in  the  body  (e.g.  drugs,  such  as  potassium  iodide, 
salicylic  acid,  santonin,  etc.). 

4.  Micturition. — The  urine  is  driven  from  the  urinary 
tubules  into  the  pelvis  by  the  pressure  of  the  secretion. 
From  the  pelvis  the  urine  is  forced  by  the  peristaltic  contrac- 
tions of  the  two  ureters  into  the  bladder.  The  bladder  is 
closed  by  the  tonic  contraction  of  the  sphincter  vesicae. 
During  micturition,  the  tonus  of  the  sphincter  is  inhibited 
and  the  contraction  of  the  detrusor  urinae  diminishes  the 
compass  of  the  bladder.  The  muscles  of  the  bladder  are 
supplied  with  nerves  from  the  sacral  and  lumbar  nerves  and 
from  the  sympathetic.      Their  centre  lies  in  the  lumbar  cord. 

8.   THE    SECRETION    OF    SWEAT 

1.  Composition  of  sweat. — Sweat  is  a  clear,  colorless  fluid 
having  a  specific  gravity  of  1.003-1.006.  Its  reaction  may 
be  acid,  neutral  or  alkaline;  it  has  a  salty  taste  and  charac- 
teristic odor.  It  contains  0.85-0.91$  solids  which  include 
0.65$  salts  (chiefly  NaCl)  and  0.24$  organic  substances 
(0.12$  urea).  The  amount  daily  secreted  is  very  variable. 
The  secretion  of  sweat  is  closely  related  to  the  regulation  of 
temperature  (see  Chapter  XIII). 

2.  Secretion  of  sweat. — The  sudoriferous  glands  are  long 
unbranching  tubules  which  form  at  the  lower  end  a  globular 
mass  (0.3-0.7  mm  in  diameter)  composed  of  a  coiled  tube. 
The  walls  of  these  coiled  tubules  have  a  single  layer  of 
cuboidal  cells. 

The  sweat  secretion  is  dependent  upon  the  nervous  system. 
Stimulation  of  the  sciatic  or  brachial  nerve  of  a  cat  produces 
sweating  of  the  paw.  It  is  not  mere  filtration  of  the  bloocT 
fluid,  but  depends  upon  the  specific  activity  of  the  gland,  as 
the  following  facts  show.  Secretion  of  sweat  does  not  take 
place  continuously,  and  twenty  minutes  after  the  amputation 
of  a  limb,  stimulation  of  the  nerve  still  produces  perspiration. 


no  HUMAN  PHYSIOLOGY 

The  nerves  of  sweat  secretion  after  leaving  the  cord  run 
through  the  sympathetic  and  later  on  join  the  nerves  going 
to  the  extremities.  The  center  for  the  secretion  of  sweat  is 
supposed  to  be  situated  in  the  cord,  for  after  the  cord  of  a 
cat  has  been  cut  in  the  cervical  region,  heat  or  dyspnoea  still 
produces  sweating  of  the  hind  legs.  A  primary  sweat 
centre  is  supposed  to  be  situated  in  the  medulla  oblongata. 
The  secretion  of  sweat  is  inaugurated  by  increase  in  tem- 
perature, asphyxia,  poisons  (pilocarpin  |,  and  also  by  psy- 
chical influences  (the  sweat  of  fear).  Atropin  inhibits  the 
secretion. 

9.   SEBACEOUS    SECRETION 

The  sebaceous  secretion  is  an  oily  substance,  consisting 
mainly  of  cholesterin  esters  of  fatty  acids.  Concerning  its 
composition  but  little  is  as  yet  known.  The  sebaceous 
secretion  oils  the  skin  and  hair. 

The  sebaceous  glands  are  composed  of  a  gland  body 
which  is  formed  by  a  number  of  saccules.  The  outer  cells 
of  these  saccules  are  small  cuboidal  cells,  while  the  inner 
cells  are  large  and  spherical  and  fill  the  whole  saccule  and, 
by  their  breaking  up,  form  the  secretion.  The  duct  leading 
from  the  gland  to  the  exterior  is  formed  by  the  continuation 
of  the  outer  hair-follicle;  it  is,  therefore,  formed  from  layers 
of  pavement  epithelial  cells. 

Concerning  the  influence  of  the  nervous  system  upon 
sebaceous  secretion  nothing  is  known. 

10.    LACHRYMAL    SECRETION 

Tears  are  composed  of  a  clear,  alkaline  salty  fluid.  They 
contain  about  \fo  solids,  chiefly  salts  (Nad).  Proteids  are 
present  in  small  quantities. 

The  lachrymal  glands  are  built  like  the  albuminous  sali- 
vary glands.  The  tears  are  secreted  continuously.  Their 
secretion  is,  however,  under  the  influence  of  the  nervous 
system;    it  is   increased   by  psychical   influences   (weeping), 


SECRETIONS  in 

also  reflex ly  when  foreign  substances  irritate  the  conjunctiva 
and  by  strong  light  falling  upon  the  eye. 

The  secretory  nerves  pass  through  the  lachrymal  nerve, 
the  subcutaneous  mallar  nerve,  and  the  cervical  sym- 
pathetic. 

The  tears  flow  through  the  ducts  of  the  lachrymal  gland 
in  the  outer  canthus  of  the  eye  into  the  conjunctival  sac  in 
the  inner  canthus  and  thereby  moisten  the  cornea  and  the 
conjunctiva  and  remove  foreign  bodies  out  of  the  conjunc- 
tival sac. 

In  the  inner  canthus  of  the  eye  the  tears  are  taken  up  by 
the  puncta  lachrymale  of  the  caruncula  lachrymalis  and  then 
flow  through  the  nasal  duct  into  the  inferior  meatus  of  the 
nose. 


11.    MILK    SECRETION 

I.  Composition  of  milk. — Milk  is  a  white  opaque  fluid 
having  an  amphoteric  reaction,  a  sweet  taste,  and  a  specific 
gravity  of  1.028-1.034.  It  is  an  emulsion  of  fat  in  which 
the  fat  droplets,  of  1.5-5/'  diameter,  are  surrounded  by 
pellicles  of  caseinogen. 

The  white  color  and  the  opaqueness  of  milk  are  due  to 
the  fact  that  the  light  is  totally  reflected  by  the  fat  droplets. 

Milk  contains  13$  solids.  The  milk  of  young  women 
contains  more  solids  than  that  of  older  women.  The  solids 
are : 

(a)  Proteids  (2.5$),  chiefly  the  nucleo-proteid  caseinogen. 
This  proteid  is  split  up  by  rennin  into  paracasein  a  pro- 
teid which  forms  with  calcium  salts  an  insoluble  double  salt 
(casein)  and  a  soluble  proteid  (whey  proteid). 

Besides  the  caseinogen,  the  milk  contains,  in  smaller 
quantities,  two  proteids  which  are  coagulated  by  heat: 
lactalbumin  and  lactoglobulin. 

(b)  Carbohydrates  (6$),  namely,  milk-sugar  or  lactose 
(see  page  21).  When  milk  stands  for  a  long  time  the  lac- 
tose  undergoes    lactic-acid  fermentation    (due  to    bacterium 


112  HUMAN  PHYSIOLOGY 

lactis).      The   lactic   acid  thus  formed  precipitates  the  case- 
inogen  (souring  of  milk). 

{c)  Fats  (4$),  in  fine  emulsions,  not  dissolved.  Besides 
the  glycerides  of  palmitic,  stearic,  and  oleic  acid,  milk 
contains  the  glycerides  of  the  lower  fatty  acids  (butyric, 
caproic,  caprylic  acid).  On  standing,  the  specifically  lighter 
fat  globules  rise  upward,  forming  the  cream. 

((/)  Cholesterin,  lecithin,  and  a  yellow  pigment  in  small 
quantities.  Besides  these  the  milk  is  said  to  contain  citric 
acid,  a  product  of  the  activity  of  the  gland. 

(*')  Salts  (0.5$),  especially  calcium  phosphate,  also  potas- 
sium chloride,  a  little  sodium  chloride,  and  a  very  little 
magnesium  sulphate  and  traces  of  iron.  The  calcium  phos- 
phate is  present  parti)'  in  solution  as  the  acid  salt  and  partly 
in  suspension  as  the  neutral  salt. 

Furthermore  the  milk  contains  gases,  chief]}'  carbon 
dioxide,  and  less  nitrogen  and  oxygen. 

2.  Conditions  of  the  secretion  of  milk. — The  secretion  of 
milk  takes  place  only  during  the  lactation  period  which  lasts 
about  ten  months. 

The  milk  gland  consists  of  15-20  single  tubular  glands, 
each  one  of  which  opens  by  a  duct  in  the  nipple.  Just  before 
opening  at  the  exterior,  the  tubules  have  a  sac-like  dilation. 

The  lactiferous  ducts  have  a  wall  of  cylindrical  epithelium. 
The  cells  of  the  gland  proper  form  a  single  layer  of  epithelial 
cells,  whose  height  varies  greatly.  When  the  ducts  are 
filled  with  secretion  these  cells  are  low,  but  when  the  ducts 
are  empty  the}'  are  cylindrical  and  filled  with  numerous  fat 
droplets.  The  cells  of  the  gland  do  not  perish  during  secre- 
tion, hence  only  form  the  secretion  and  excrete  it. 

During  the  first  days  after  delivery  there  are  present  in 
the  milk  the  so-called  colostrum  corpuscles  which  are 
nucleated  rudiments  of  cells  containing  many  fat  droplets. 

The  nervous  system  has  an  influence  upon  milk  secretion, 
for  the  emotions  can  alter  the  quantity  and  character  of  the 
milk.      As  to  the  secretory  nerves  authors  differ. 

Nourishment  has  an  effect  upon  the  quantity  and  com- 


SECRETIONS  XI, 


position  of  the  milk.      A  meal  rich  in  proteids  increases  the 
proteids  and   fat  of  milk;    carbohydrate  food   increases  the 
lactose,  but  fatty  food  does  not  increase  the  fat  of  the  milk 
Caseinogen   and  lactose  are  formed  in   the   milk  glands,  for 
they  do  not  occur  in  the  blood. 

Frequent  discharge  of  the  milk  from  the  glands  by  nursing 
the  child  or  by  milking  increases  the  milk  secretion. 


CHAPTER    VIII 

NUTRITION 

1.   FOODSTUFFS    (ALIMENTARY    PRINCIPLES) 

FOODSTUFFS  are  substances  which  the  body  must  take  up 
in  order  to  maintain  its  material  existence,  i.e.  substances 
by  which  the  body  can  rebuild,  restore,  and  replace  the 
parts  which  have  been  changed  and  used  up  by  the  vital 
processes. 

We  may  divide  foodstuffs  into  the  following  classes: 

1.  Those  not  furnishing  energy,  i.e.  foodstuffs  which  can- 
not impart  energy  to  the  body  (water  and  salts). 

2.  Those  furnishing  energy,  i.e.  substances  rich  in  poten- 
tial energy,  which  by  their  physiological  combustion  furnish 
the  body  with  the  energy  it  needs  for  its  functions.  This 
class  includes: 

[a)  Nitrogenous  substances — proteids. 

(li)   Non-nitrogenous  substances — carbohydrates  and  fats. 

The  energy-yielding  substances  are  sometimes  called 
"foodstuffs  "  in  a  narrower  sense. 

Strictly  speaking  the  inhaled  oxygen  also  belongs  to  the 
class  of  energy-yielding  foodstuffs,  for  it  is  only  by  its  union 
with  the  above-named  energy-yielding  foodstuffs  that  their 
chemical  potential  energy  can  be  set  free  and  can  be  used 
by  the  body. 

The  water  serves  to  replace  the  water  lost  in  the  secre- 
tions, faeces,  and  expired  air.  The  water  formed  in  the  body 
by  the  combustion  of  organic  substances  containing  hydrogen 
can  replace  only  a  small  amount  of  the  loss,  for  the  amount 
so  formed   is  only  about  350  cc  in  24  hours,  while  an   adult 

114 


NUTRITION  115 

person  needs  2-2.5  litres.  The  amount  of  water  needed  is 
determined  by  the  amount  lost  in  the  urine,  sweat,  and 
expired  air. 

The  salts  of  the  food  in  part  replace  the  salts  taken  from 
the  tissue  fluid  by  the  excretory  organs,  and  in  part  furnish 
material  for  the  formation  of  organic  substances  (nuclein, 
haemoglobin).  The  following  are  the  salts  necessary  as 
foods : 

The  phosphates  of  the  alkalies  are  used  in  the  building  of 
the  tissues.  Only  in  the  presence  of  potassium  phosphate 
can  the  cell  substance  regenerate  itself. 

■Calcium  and  magnesium  phosphate  serve  chiefly  in  build- 
ing up  the  skeleton.     - 

Salts  of  iron  are  used  in  the  formation  of  the  red  blood 
pigment. 

The  need  of  iron  seems,  as  a  rule,  to  be  completely  satisfied  by 
the  organic  iron  (nucleo-proteids  containing  iron)  which  is  taken 
up  with  the  other  foodstuffs  so  that  no  other  iron  salts  need  to  be 
taken. 

The  salts  enumerated  thus  far  are  found  in  sufficient 
quantity  in  the  foods  generally  taken,  so  that  they  do  not 
need  to  be  specially  added.  The  case  is,  however,  different 
with 

Sodium  chloride,  which  not  only  serves  to  replace  the  loss 
from  the  body  fluids,  but  serves,  at  the  same  time,  as  a  con- 
diment (see  page  1 18)  and  is  therefore  eaten  in  much  larger 
quantities  than  is  really  necessary.  The  average  amount  of 
NaCl  taken  by  the  adult  is  about  17  grams,  while  the  real 
need  is  only  about  2  grams. 

The  need  of  sodium  chloride  is  greater  among  people  living 
upon  vegetable  food  (Negro)  than  among  those  eating  flesh 
(Samoids,  Tunguses).  The  reason  for  this  has  been  sought  in  the 
greater  amount  of  potassium  salts  of  the  vegetables.  The  potas- 
sium carbonate  acts  upon  the  sodium  chloride  in  the  body  so  that 
sodium  carbonate  and  potassium  chloride  are  formed.  These 
substances  are  excreted  by  the  kidneys.  Hence  by  the  partaking 
of  potassium  salts  the  excretion  of  sodium  and  chlorine  is  increased 
and  therefore  more  sodium  and  chlorine  must  be  taken  up  in  the 
food. 


Il6  HUMAN   PHYSIOLOGY 

The  salts  of  the  foodstuffs  not  only  serve  to  replace  the 
same  salts  in  the  body,  but  also  to  form  other  salts  present 
in  the  organism  which  are  not  taken  up  with  the  food  (e.g. 
the  alkali  carbonates).  Continued  lack  of  salt  in  the  food 
(salt-hunger)  results  in  death,  even  though  food  be  given 
in  sufficient  quantity. 

Of  the  combustible  foodstuffs,  proteids  serve  to  replace  the 
body-proteids  destroyed  by  the  physiological  combustion. 
There  is  no  nitrogenous  substance,  besides  proteid,  which  can 
supply  the  body  with  material  for  building  up  its  proteids. 
Hence  proteids  are  absolutely  necessary  for  building  up  the 
tissues.  But  all  proteids  arc  not  capable  of  doing  this,  for 
the  albuminoids  (gelatin)  cannot  entirely  replace  the  proteids 
of  the  body.  Otherwise  it  appears  that  the  various  true 
proteids  (simple  and  combined  proteids,  proteoses)  are  of 
equal  value  as  food  for  replacing  the  body  proteids.  At  all 
events,  it  is  not  necessary  that  the  same  kinds  of  proteids 
found  in  the  body  should  be  found  in  the  food.  For  exam- 
ple, the  haemoglobin  and  nucleo-albumins  in  the  body, 
originate,  no  doubt,  from  the  union  of  other  proteids  with 
iron  or  phosphoric  acid.  The  albuminoids  of  the  body  are 
also  formed  from  the  true  proteids,  not  from  the  albuminoids 
of  the  food. 

Proteids  contain  all  the  elements  needed  for  replacing 
organic  substances  in  the  body;  fats  and  carbohydrates  con- 
tain only  a  part,  viz.  carbon,  oxygen,  and  hydrogen. 
Hence  proteids  alone  must  be  sufficient  to  satisfy  the  demand 
for  combustible  food  for  the  body.  We  can,  indeed,  feed 
the  carnivorous  animals  on  an  exclusive  proteid  diet.  This 
cannot  be  done  with  man  and  vegetable-eating  animals,  for 
the  quantity  of  proteid  necessary  to  support  life  cannot  be 
digested  by  them. 

The  fats  and  carbohydrates  serve  as  material  for  combus- 
tion which  furnishes  the  body  with  energy  for  heat  production 
and  for  work.  In  metabolism,  gelatin  plays  the  same  part. 
It  is  often  stated  that  fat  serves   mainly  for  heat  production, 


NUTRITION  117 

while  carbohydrates  furnish  energy  for  work,  but  there  is,  in 
this  respect,  no  such  fundamental  difference  between  them. 

As  nutrition  on  an  exclusively  proteid  diet  is  at  least 
theoretically  possible,  we  can  express  the  amount  of  energy- 
yielding  foodstuffs  necessary  for  nutrition  in  terms  of  the 
amount  of  proteids  needed.  For  a  man  of  70  kg  body 
weight,  the  amount  of  proteids  must  be  about  700  grams  a 
day. 

A  part  of  this  food  must  be  proteid,  it  being  absolutely 
necessary.  This  amounts  to  about  70  g  per  day.  It  has 
been  observed  that  the  body  can  get  along  with  a  much 
smaller  quantity  of  proteids  (40  g  per  day),  but  such  experi- 
ments only  lasted  for  a  very  short  time,  hence  it  is  a  ques- 
tion whether  the  body  can  be  nourished  for  a  great  length 
of  time  with  such  a  small  amount  of  proteid. 

After  we  have  supplied  the  absolutely  necessary  proteid, 
the  remainder  of  the  food  needed  can  be  taken  in  the  form 
of  proteid,  gelatin,  fat,  or  carbohydrate  or  as  a  mixture  of 
these  substances.  The  proportion  in  which  the  foods  can, 
in  this  case,  replace  each  other  is  based  upon  the  law  of 
isodynamics,  which  states  that  such  quantities  of  combustible 
foodstuffs  as  furnish  the  same  amount  of  energy  during  their 
physiological  combustion  are  equivalent  (see  Chapter  XIII). 
In  round  numbers  the  following  quantities  furnish  the 
same   amount  of  energy:    2.3   g  proteid  =1    g  fat  =  2.3  g 

carbohvdrates. 

1 

For  an  exact  application  of  the  law  of  isodynamics  in  the  prac- 
tical study  of  nutrition  it  must  be  borne  in  mind  that,  in  meta- 
bolism, the  proteids  behave  differently  from  the  fats  and 
carbohydrates  (see  Chapter  XII). 

As  a  diet,  the  following  is  necessary: 

Proteid.  Fat.        Carbohydrates. 

Resting  man 100  g  60  g         400  g 

woman 90  g  40  g         350  g 

Working  man 130  g        100  g         500  g 

The  absolute  amount  needed  by  old  people  and  children 
is  less.     But  if  the  food  necessary  for  each  kilogram  of  body 


nS  HUMAN   PHYSIOLOGY 

weight  is  considered,  it  will  be  found  that  children  need  a 
larger  amount  than  adults.  This  is  due  to  two  causes: 
first,  a  growing  body  needs  relatively  more  food  than  an 
adult,  and  secondly,  the  metabolism  of  children  is  relatively 
greater  than  that  of  adults  because  of  the  greater  proportion 
of  surface  (thereby  greater  loss  of  heat)  compared  to  the 
heat  producing  mass  (see  Chapter  XIII). 

For  one  kilogram  of  body  weight  the  following  amounts 
are  necessary: 

Age.                                             Proteid.              Fat.  Carbohydrates. 

2-6  years 3-7  g  3-°g  'O.og 

7-15  years 2.8  g  1.5  g  9.0  g 

Adult 1.6  g  0.8  g  8.0  g 

Besides  the  foodstuffs  we  still  take  up  man)-  substances 
which  are  not  necessary  for  the  maintenance  of  the  body, 
but  which  are,  nevertheless,  of  physiological  importance. 
They  are  the  condiments.  They  include  substances  having 
a  specific  taste  and  odor  which  stimulate  the  nervous  system, 
increase  digestion,  aid  circulation,  etc.  Under  this  class 
we  may  mention  spices  and  certain  alkaloids  (caffein  in  tea 
and  coffee,  theobromin  in  cocoa,  nicotin  in  tobacco). 

There  are  still  other  organic  substances  (e.g.  vegetable 
acid,  many  alcohols)  which  are  also  burned  in  the  body  and 
can  therefore  be  regarded  as  energy-yielding  foodstuffs  even 
though  they  are  not  necessary  for  the  body.  As  far  as  ethyl 
alcohol  is  concerned,  its  worth  as  a  food  is  doubtful  since  it 
acts  as  a  violent  poison  and  its  frequent  use  produces  morbid 
changes  in  almost  all  the  organs  of  the  body. 

2.    FOODS 

The  foods  furnished  us  by  nature  are  mixtures  of  the  food- 
stuffs.     They  may  be  classified  as: 

1.  Food  from  the  animal  world. 

2.  Food  from  the  vegetable  world. 

The  composition  of  the  chief  foods  is  as  follows: 


NUTRITION  119 

PERCENTAGE   COMPOSITION   OF   CERTAIN   FOODS. 


Proteids 


Fat. 


Carbo- 
hydrates I 


Water.        Salt. 


Cellu- 


I.  Animal  Foods. 


Lean  beef 

Fat  pork 

Shellfishes 

Salmon 

Human  milk.  . 

Cow  milk 

Eggs 


11. 


20.0 

14.5 
17.0 

21-5 

2.5 

3-5 
12.5 

Vegetable  Foods. 


i-5 

0.9 

37-5 

0.6 

0.5 

12.5 

4.0 

6.0 

4.0 

4.o 

12.0 

1.0 
1.0 
i-5 
i-5 

o-5 
0.7 
1 .0 


Leguminous  foods  (beans). 

Rice 

Fine  wheat  flour 

Rye  flour 

White  bread 

Rye  bread 

Potatoes 

Cabbage 

Asparagus 

Fruit 


24.5 

2.0 

52.0 

12.5 

3-5 

6.5 

1.0 

7«-5 

12.5 

1 .0 

10. 0 

1.0 

72.0 

13-5 

0.5 

11  5 

2.0 

69-5 

14.0 

i-5 

7.0 

o-5 

52-5 

35-5 

1 .0 

6.0 

0.5 

49.0 

40.5 

1  0 

2.0 

0.2 

20.7 

75-o 

1.0 

2.5 

°-5 

10.5 

88.0 

1 .0 

2.0 

0.3 

2-5 

89.0 

0.5 

0.5 

10. 0 

85.0 

0.5 

6.0 
4.0 
0.3 

i-S 
0.3 
0.6 
1.0 

i-5 
1 .0 

4.0 


Generally  the  animal  foods  predominate  in  proteids  and 
fat.  Lean  beef  consists  almost  entirely  of  proteid,  and  can 
therefore  practically  be  regarded  as  a  pure  proteid  food. 
Butter  is  nearly  altogether  fat.  Of  the  animal  foods  we  find 
carbohydrates  only  in  the  milk  and,  in  very  small  quan- 
tities, in  the  liver  (lactose  and  glycogen  respectively). 

The  vegetables  chiefly  contain  the  carbohydrates  and  but 
little  or  no  fat.  Proteids  are  found  in  all  vegetables, 
especially  in  the  legumes. 

The  following  details  deserve  mention : 

The  muscles  are  called  beef.  They  consist  of  the  muscle  fibre 
proper  and  connective  tissue;  the  first  contains  true  proteids,  the 
other  a  substance  yielding  gelatin.  The  real  proteid  value  of 
meat  is  determined  by  the  proportion  of  fibres  and  connective 
tissue  present. 

The  amount  of  fat  found  in  beef  varies  much  and  depends  upon 
the  feeding. 

The  manner  of  preparation  (boiling,  roasting,  etc.)  does  not 
alter  the  value  of  beef  as  a  food.  Boiled  beef  (meat  from 
which  soup  is  made)  has  still  the  same  food  value  as  the  red  or 
roasted  meat,  but  is  slightly  less  palatable  because  the  extrac- 
tives which  give  it   taste  have  been  removed.      In   beef  tea   (or 


120  HUMAN  PHYSIOLOGY 

beef  soup)  there  are,  excepting  the  floating  fat  droplets  and  a 
little  gelatin,  no  combustible  foodstuffs  and  it  can  therefore  not 
be  regarded  as  a  strengthening  food.  It  contains  besides  the  salts 
(potassium  phosphate)  the  extractives  (kreatin,  xanthin)  which 
impart  to  it  a  delicious  flavor  and  a  stimulative  activity.  It  is 
only  a  condiment. 

Besides  the  beef  of  muscle,  other  animal  organs  are  used  as  food; 
some  of  these  also  contain  large  quantities  of  proteids  and  gelatin. 

Human  milk  contains  more  sugar  but  less  proteids  and  salts 
than  cow  milk.  To  render  cow  milk  like  human  milk  (which  is 
necessary  for  the  nursing  child),  it  must  be  diluted  with  water  and 
lactose  must  be  added. 

The  chief  proteid  of  milk  is  caseinogen.  The  caseinogen  of 
cow  milk  is  coagulated  by  rennin  in  larger  flakes  than  that  of 
human  milk  and  is  therefore  less  accessible  to  the  action  of  the 
digestive  fluids.  Hence  children  frequently  cannot  use  cow  milk. 
This  difference  in  coagulation  is  not  due  to  any  chemical  differ- 
ence in  the  caseinogen,  but  to  the  different  amounts  of  calcium 
salts  present  in  the  milk. 

The  calcium  salts  of  milk  are  used  to  build  up  the  skeleton  of 
the  growing  organism. 

The  cream  which  rises  to  the  top  when  milk  stands,  or  which 
can  be  centrifugalized  from  milk,  furnishes  butter.  The  butter  is 
obtained  by  beating  the  cream  which  breaks  the  caseinogen 
pellicles  of  the  fat  globules  so  that  the  fat  globules  flow  together. 

Unsalted  butter  consists  chiefly  of  fat,  90^,  mainly  glycerides 
of  oleic,  palmitic,  and  stearic  acids  and,  in  smaller  quantities,  of 
butyric,  caproic,  and  eaprylic  acids;  it  further  contains  8$  water 
and  casein  (2^),  lactose  and  salts.  The  buttermilk  which  is  left 
can  still  be  regarded  as  good  food,  as  it  contains  much  proteid 
(3-4$)  and  sugar  (4$). 

When  milk  is  coagulated  by  rennin,  cheese  (casein  coagulate) 
is  formed;  the  residue  is  called  whey.  The  casein  incloses  the 
fat  globules,  and  after  the  whey  has  been  removed  it  undergoes  a 
putrefactive  process,  the  ripening  of  cheese.  By  this  process  part 
of  the  proteids  are  peptonized,  part  are  decomposed  into  amido 
acids:  besides  this,  fatty  acids  are  set  free.  Cheese  is  a  valuable 
food  because  it  contains  much  proteid  and  fat.  Fat  cheese  con- 
tains 25$  proteid  and  30.5$  fat;  poor  cheese  contains  34$  proteid 
and  1  1.5^  fat. 

The  white  of  egg  contains  only  egg  albumin;  the  yolk  of  egg 
contains,  besides  the  proteids  (vitellin),  chiefly  fat,  lecithin,  and 
cholesterin. 

All  vegetables  contain  a  substance  not  found  in  the  animal 
food — cellulose  or  wood   fibre.      This  is  but  slightly  or  not 


NUTRITION  I2i 

at  all  digested  in  the  intestine  of  man,  but  stimulates  the 
peristaltic  movements,  probably  by  mechanical  stimulation 
of  the  intestinal  muscles.  This  causes  vegetables  to  pass 
through  the  intestine  more  rapidly  than  animal  food.  The 
food  of  the  vegetables  is  inclosed  in  cellulose  coats  and 
hence  is  not  directly  accessible  to  the  digestive  fluids.  By 
preparing  the  vegetable  foods  (grinding,  cooking,  baking) 
the  cellulose  envelopes  are  burst  and  the  food  proper  can 
then  be  readily  acted  upon  by  the  digestive  fluids. 

As  a  food  the  vegetable  proteid  is  of  equal  value  to  the 
animal  proteid.  The  carbohydrates  of  vegetables  are  gen- 
erally present  in  the  form  of  starch,  and,  to  a  smaller 
extent,  as  sugar  (dextrose,  fructose,  cane-sugar,  maltose). 
Starch  is  rendered  more  digestible  by  boiling,  which  causes 
it  to  swell. 

Grinding  changes  the  grain  foods  to  fine  particles — flour.  From 
this  the  cellulose  envelopes  (bran)  are  removed  by  sifting.  The 
more  bran  the  flour  contains,  the  richer  it  becomes  in  proteid,  for 
the  richest  proteid  layer  of  the  grain  lies  just  below  the  cellulose 
envelope.  The  flour  is  used  in  baking  bread,  etc.  The  baking 
is  made  possible  by  a  proteid,  called  gluten.  The  leaven  (yeast) 
added  to  the  dough,  produces  carbon  dioxide  by  its  sugar  fermen- 
tation which  loosens  the  bread.  In  many  kinds  of  bread  (black 
bread,  graham  bread),  flour  rich  in  bran  is  used,  and  the  cellulose 
of  the  bran  aids  the  peristalsis  of  the  intestine  and  prevents  con- 
stipation. 

The  leguminoses  are  peculiar  because  of  their  large  amount  of 
proteid.  They  contain  no  gluten  and  can  therefore  not  be  used 
in  baking.  They  contain,  however,  a  proteid  called  legumin 
which  forms,  when  boiled  with  lime  water,  an  insoluble  compound 
with  calcium.  Hence  they  must  always  be  boiled  in  soft  water 
(containing  no  lime),  otherwise  they  remain  hard. 

To  obtain  nourishment  from  such  foods  as  greens,  cabbage, 
lettuce,  fruits,  which  are  rich  in  water,  a  large  quantity  must  be 
taken.  Thev  are  therefore  not  used  as  a  principal  food  but  only 
as  supplemental  to  others,  and  serve  as  condiments  because  of 
their  flavors.  They  also  furnish  the  cellulose  necessary  for  the 
peristalsis. 

As  to  the  question  whether  animal  food  or  plant  food  is 
more  suitable  for  man,  it  ma}'  be  stated  that  a  mixed  diet 
consisting-  of  one-third  animal  and  two-thirds  vegetable  food 


122  HUMAN  PHYSIOLOGY 

is  most  suitable.  Animal  food  is  not  suitable  as  an  exclusive 
diet  because  it  contains  no  carbohydrates;  on  the  other 
hand,  the  vegetables  contain  too  little  proteid  and  no  fat. 
Also  the  structure  of  the  digestive  organs  of  man  indicates 
that  he  is  intermediate  between  the  exclusive  carnivorous 
and  herbivorous  animals.  In  flesh-eating  animals  the  length 
of  the  intestine  is  about  five  times  that  of  the  body  (reckoned 
from  mouth  to  anus),  in  the  plant-eaters  it  is  more  than 
twenty  times  this  length.  The  great  length  of  the  intestine 
of  herbivorous  animals  serves  to  offset  the  more  rapid  move- 
ment of  the  food,  in  order  that  the  food  may  be  sufficiently 
acted  upon  and  absorbed.  As  the  length  of  the  intestine  of 
man  is  about  ten  times  that  of  his  body,  he  is  intermediate 
between  the  carnivorous  and  herbivorous  animals. 

As  can  be  observed  in  vegetarians,  man  can  indeed  be  nourished 
by  vegetable  foods  only,  but  there  are  no  sufficient  reasons  for 
excluding  meat  altogether  from  our  diet.  An  exclusive  meat  diet 
cannot  be  endured  by  man  for  any  great  length  of  time  because 
of  the  resulting  disturbance  in  digestion. 

As  many  of  the  foods  supplied  us  by  nature  are  odorless  and 
tasteless,  we  spice  them.  The  physiological  significance  of  spices 
lies  in  the  fact  that  they  increase  the  secretion  of  the  digestive 
juices,  thereby  aiding  digestion  and  stimulating  the  appetite. 

Of  the  various  drinks,  which  are  chiefly  spices  (coffee,  tea, 
cocoa,  alcoholic  drinks),  cocoa  may  also  be  considered  as  a  fund, 
because  it  contains  much  proteid  (12$),  carbohydrates  (i^fc),  and 
fat  (in  cocoa  not  freed  of  its  fat,  49$).  Beer  also  contains  food- 
stuffs (proteid  up  to  0.8$,  carbohydrates  5-6$).  but  it  can  never- 
theless not  be  classified  as  a  food,  for.  taken  in  large  quantities, 
the  harmful  effects  of  alcohol  are  manifested.  Besides  this,  the 
cost  <>f  beer  is  much  too  high  in  proportion  to  its  food  value. 

Certain  sensations- — hunger  and  thirst — may  be  regarded 
as  the  stimulations  for  taking  up  food  and  drink.  (See 
Chapter  XXVI.) 


CHAPTER    IX 
THE    DIGESTION    OF   THE    FOODSTUFFS 

By  digestion  most  of  the  foodstuffs  undergo  physical  and 
chemical  changes  by  which  they  are  prepared  for  absorption 
into  the  blood.  Only  a  few  foodstuffs,  e.g.  water,  salts, 
grape-sugar,  can  become  part  of  our  body  without  any 
change.  The  most  important  alimentary  principles,  pro- 
teids,  fats,  and  many  carbohydrates  cannot  be  absorbed  in 
the  form  in  whch  they  are  furnished  by  nature. 

The  digestion  proper  is  preceded  by  a  mechanical  tritura- 
tion of  the  solid  foods  by  biting  and  chewing. 

Digestion  itself  consists  of  rendering  the  insoluble  or 
slightly  soluble  and  non-dialyzable  foodstuffs  soluble  and 
dialyzable.  This  is  brought  about  by  the  digestive  ferments 
which,  by  hydrolytic  splitting  up,  form  smaller  molecules 
from  the  large  molecules  of  the  native  foods.  In  this 
manner  proteids  are  split  up  into  proteoses ;  starch  into 
sugar;   fats  into  glycerin  and  fatty  acid. 

The  organ  in  which  the  digestion  is  carried  on  is  the 
alimentary  canal  (tractus  intestinalis) ;  it  consists  of  mouth 
and  esophagus,  stomach,  small  and  large  intestine. 

1.   DIGESTION    IN    THE    MOUTH 

i.   Mechanical   changes    of   food   in   the   mouth. — The 

mechanical  processes  in  the  mouth  consist  of  cutting  (biting), 
chewing,  and  sucking. 

Biting  serves  to  cut  off  proper  portions  of  the  food.  The 
morsel  is  ground  up  more  or  less  by  chewing  and,  being 

123 


124  HUMAN  PHYSIOLOGY 

soaked  by  the  saliva,  forms  a   pulp  so  that  the  food  is  soft, 
lubricated,  and  suitable  for  deglutition. 

Biting  and  chewing  are  caused  by  the  movement  of  the 
upper  and  lower  teeth  against  each  other. 

The  lower  jaw  is  raised  (turning  around  a  horizontal  axis  pass- 
ing through  both  limbs  of  the  jawj  by  the  masseter,  temporal  and 
internal  pterygoid  muscles  of  both  sides  of  the  head.  It  is  lowered 
by  the  digastric,  mylohyoid  and  geniohyoid.  During  the  lower- 
ing of  the  jaw,  the  hyoid  bone  must  be  fixed;  this  is  performed 
by  the  omo-,  sterno-,  and  thyro-hyoid  and  the  sternothyroid. 
The  lower  jaw  is  moved  forward  in  a  horizontal  direction  by  the 
two  external  pterygoids;  to  the  left,  by  the  right  external  ptery- 
goid; and  to  the  right,  by  the  left  external  pterygoid.  The  morsel 
is  held  between  the  teeth,  during  chewing,  by  the  buccinator  from 
the  outside  and  by  the  tongue  from  the  inside. 

The  tongue  is  pulled  forward  and  downward  by  the  genio- 
glossus,  while  it  is  pulled  downward  and  backward  by  the  hyo- 
glossus,  and  upward  and  baekward  by  the  palato-  and  stylo- 
glossus. 

The  tongue  is  composed  of  vertical,  longitudinal,  and  diagonal 
fibres.  By  the  combination  of  their  contractions,  it  can  assume 
many  varying  position-. 

Sucking  serves  to  take  up  liquid  food.  By  the  sucking, 
a  negative  pressure  is  produced  in  the  mouth,  and  the  fluid 
to  be  taken  up  is  thus  sucked  in. 

Sucking  is  produced  in  one  of  two  ways: 

(a)  By  inspiration  after  separating  the  nasal  passage  from 
the  pharyngeal  cavity  by  elevating  the  soft  palate. 

(6)  After  the  mouth  cavity  is  separated  from  the  pharyn- 
geal cavity  by  pressing  the  posterior  part  of  the  tongue 
against  the  palate,  the  lower  jaw  is  depressed  and  the 
tongue  is  pulled  backward  and  downward  (pure  mouth-suc- 
tion). 

The  negative  pressure  in  the  mouth  during  pure  mouth-suction 
may,  by  repeated  sucking,  be  made  as  low  as  700  mm  Hg  below 
atmospheric  pressure. 

2.  Chemistry  of  digestion  in  the  mouth. — Digestion  in 
the  mouth  only  affects  starch.  This  is  split  up  by  the  ptyalin 
of  the  saliva,  the  animal  diastase,  into  sugar. 

The  animal   diastase  differs  from  that  of  the  plants  (the  sugar- 


THE   DIGESTION   OF    THE  FOODSTUFFS  125 

forming  ferment   of  sprouting  barley)  in  that   the  former  is   most 
active  at  400,  while  the  latter  acts  most  energetically  at  6o°. 

Ptyalin  is  a  proteid-like  body.  It  can  be  obtained  for  experi- 
ments in  digestion  from  fresh  or  dried  salivary  glands  by  extracting 
the  gland  with  water  or  glycerin. 

Ptvalin  acts  best  in  neutral  solutions.  It  is  rendered  in- 
active and  is  destroyed  by  alkalies  and  especially  by  mere 
traces  of  free  mineral  acids.  Organic  acids  only  inhibit  its 
activity.  Ptyalin  is  destroyed  by  temperatures  above  6o°. 
Maltose  is  the  chief  product  in  the  digestion  of  starch  by 
ptyalin,  only  little  dextrose  being  formed.  According  to 
later  researches,  the  small  amount  of  grape-sugar  is  not 
formed  by  the  direct  action  of  ptyalin  upon  starch,  but  is 
formed  from  maltose  by  the  activity  of  a  second  ferment, 
glucase.      Ptyalin  itself  forms  maltose  only. 

In  this  formation  of  maltose  from  starch,  a  number  of  in- 
termediate products,  called  dextrins,  are  formed.  These 
dextrins  differ  from  each  other  in  their  behavior  towards 
iodine  and  are  called  amylo-,  erythro-,  and  achroo-dextrins, 
according  as  they  color  blue  or  red  or  do  not  color  with 
iodine. 

The  saliva  of  carnivorous  animals  contains  no  ptyalin;  in  this 
case,  the  saliva  only  seems  to  moisten  and  lubricate  the  dry  food. 
Mammals  living  in  the  water  and  not  eating  dry  food  have  no 
salivary  glands. 

Saliva  also  serves  to  moisten  and  clean  the  mouth. 

3.  Deglutition. — By  deglutition  or  swallowing,  the  chewed 
food  is  moved  into  the  stomach. 

The  bolus  is  moved  from  the  anterior  end  of  the  tongue 
along  the  hard  palate  to  the  anterior  pillars  of  the  fauces. 
By  the  stimulation  of  the  sensory  nerves  ending  in  the 
mucous  membrane  at  this  part,  a  reflex  action  is  produced 
which  results  in  a  forcible  contraction  of  the  mylohyoid  and 
hyoglossal  muscles.  By  this  the  bolus  is  pushed  backward 
into  the  esophagus. 

In  order  that  food  shall  only  escape  backward,  the  pharyngeal 
cavity  must  be  separated  from  the  mouth,  nose,  and  larynx.  This 
is  accomplished  as  follows: 


126  HUMAN  PHYSIOLOGY 

The  opening  into  the  mouth  is  closed  by  the  posterior  part  of 
the  tongue  being  pressed  against  the  hard  palate  and  against  the 
neighboring  anterior  pillars  of  the  fauces.  The  nasal  cavity  is 
separated  from  the  pharynx  by  the  elevating  of  the  soft  palate  (by 
means  of  the  levator  palati  mollis),  by  the  arching  of  the  posterior 
walls  of  the  pharynx  (by  means  of  the  superior  constrictors  of  the 
pharynx),  and  by  the  meeting  of  the  two  posterior  pillars  of  the 
fauces  at  the  median  line.  The  opening  into  the  larynx  is  closed 
by  the  elevation  of  the  larynx  by  means  of  the  mylohyoid  and  the 
geniohyoid  and  the  digastric,  to  such  an  extent  that  it  can  be 
covered  by  the  root  of  the  tongue  and  the  epiglottis. 

The  first  act  of  deglutition  here  described  may  occur  with 
so  much  force  that  by  means  of  it  the  food  reaches  the 
stomach.  This  is  especially  true  for  liquids  and  soft  foods. 
Only  solid  and  dry  foods  remain  in  the  pharynx  or  upper 
part  of  the  esophagus  till  the  second  step  in  deglutition 
carries  them  downward. 

The  second  part  of  deglutition  consists  of  a  peristaltic 
movement,  that  is,  a  constriction  of  the  esophagus  beginning 
at  the  top  and  travelling  downward.  The  pharynx  first 
constricts  by  means  of  its  constrictors,  then  the  esophagus 
by  means  of  the  constriction  of  the  circular  muscles.  Thus 
the  parts  of  the  pharynx  and  esophagus,  successively  con- 
stricted, push  the  bolus  toward  the  stomach. 

The  propagation  of  the  contraction  from  one  part  of  the 
esophagus  to  another  does  not  take  place  by  the  direct  conduction 
in  the  muscles,  but  is  dependent  upon  the  central  nervous  system. 
After  the  esophagus  has  been  cut  across,  the  wave  of  contraction 
is  set  up  in  the  lower  part  when  it  has  ceased  in  the  upper 
segment. 

The  innervation  of  the  muscles  of  the  buccal  and  pharyngeal 
cavities  is  brought  about  by: 

i.  The  third  branch  of  the  trigeminus:  masseter,  temporal, 
internal  and  external  pterygoid,  tensor  palati  mollis,  mylohyoid, 
anterior  belly  of  the  digastric, 

2.  The  facial:  muscles  of  the  face,  buccinator,  posterior  belly 
of  the  digastric,  levator  palati  mollis,  azygus  uvulae. 

3.  The  glossopharyngeal  and  vagus:  stylopharyngeal,  con- 
strictors of  pharynx  and  muscles  of  esophagus. 

4.  Hyp<  »gl<  »SSUS  :  the  tongue-muscles  collectively  and  the  genio- 
hyoid and  thyrohyoid. 

The  nerve-centres  which  govern  the  processes  of  chewing,  suck- 


THE  DIGESTION   OF   THE  FOODSTUFFS  127 

ing  and  swallowing  lie  in  the  medulla   oblongata.      (See  Chapter 
XVIII. ) 

2.   GASTRIC    DIGESTION 

1.  The  movements  of  the  stomach. — Both  the  cardiac 
and  pyloric  openings  of  the  stomach  are  generally  closed 
by  the  tonic  contraction  of  the  sphincters.  During  the  act 
of  deglutition,  the  cardiac  aperture  opens  by  the  relaxation 
in  the  tonus  of  its  muscles  when  the  peristaltic  contraction 
has  reached  the  lower  end  of  the  esophagus.  The  pylorus 
opens  and  closes  to  admit  part  of  the  contents  of  the  stomach 
into  the  duodenum. 

The  stomach  consists  of  two  parts : 

(1)  The  fundus  with  feeble  muscles. 

(2)  The  antrum  with  strongly  developed  muscles.  The 
two  parts  can  be  separated  from  each  other  by  a  sphincter- 
like muscle. 

Corresponding  to  the  distribution  of  the  muscles,  the 
movements  of  the  pyloric  part  of  the  stomach  are  much 
stronger  than  those  of  the  fundus.  In  the  antrum,  the 
pressure  caused  by  the  contraction  of  the  muscles  may  be  as 
high  as  130  mm  Hg;  the  pressure  in  the  fundus  only  35  mm. 

The  movements  of  the  fundus  serve  to  mix  the  food  with 
the  gastric  juice,  the  movements  of  the  antrum  serve  to 
empty  the  contents  of  the  stomach  into  the  duodenum. 

The  length  of  time  during  which  the  different  foods  remain 
in  the  stomach  varies  greatly.  Fluid  and  soft  foods  are 
forced  into  the  intestine  soon  after  being  swallowed,  but 
solid  food  remains  for  a  longer  time  in  the  stomach.  The 
last  particles  of  food  have  left  the  stomach  7-8  hours  after 
a  meal. 

Even  the  excised  stomach  can  execute  movements.  The 
normal  stimulation  for  the  muscles  of  the  stomach  appears 
therefore  to  be  due  to  the  nerve  plexuses  in  its  walls ;  but 
the  central  nervous  system  influences  these  movements. 
There  are  motor  and  inhibitory  nerve-fibres  for  the  stomach. 
These  fibres  run  in  the  vagus    and    sympathetic    and  their 


128  HUMAN   PHYSIOLOGY 

centres   lie  in   the   medulla,   the  corpora  quadrigemina,  and 
the  spinal  cord. 

Vomiting  is  the  emptying  of  the  contents  of  the  stomach  after 
the  cardiac  sphincter  has  opened.  It  is  brought  about  mainly  by 
the  contraction  of  the  diaphragm  and  the  muscles  in  the  abdominal 
walls,  bv  which  the  intra-abdominal  pressure  is  increased  to  such 
an  extent  that  vomiting  results.  To  a  limited  extent  the  antrum 
also  takes  part  in  vomiting. 

Vomiting  is  brought  about  reflexly  (stimulation  of  the  sensory 
nerve  in  the  stomach  by  abnormal  substances)  or  by  drugs  which 
directly  affect  the  vomiting  centre  in  the  medulla  or  by  psychical 
influences  (nauseating  sights). 

2.  Chemistry  of  gastric  digestion. — When  the  food  has 
reached  the  stomach  it  is  still  further  subjected  to  the  action 
of  salivary  ferments  (amylolytie  period  of  gastric  digestion) 
for  about  half  an  hour.  After  this,  the  secretion  of  the  acid 
gastric  juice  stops  the  action  of  the  ptyalin.  Then  the 
action  of  the  gastric  juice  begins. 

The  active  constituents  of  gastric  juice  are  pepsin,  hydro- 
chloric acid,  and  rennin.  The  gastric  juice  digests  proteids, 
inverts  cane-sugar,  and  curdles  milk,  but  does  not  act  upon 
fats. 

(a)  Proteid  digestion. — Proteid  digestion  is  brought  about 
by  the  action  of  free  hydrochloric  acid  and  of  the  pepsin  ;  by 
means  of  these  the  proteids  of  the  food  are  split  up  into 
albumoses  and  peptones. 

The  role  of  the  hydrochloric  acid  in  proteid  digestion  is 
twofold : 

hirst,  it  causes  the  proteid  bod}'  to  swell  more  or  less  and 
thereby  facilitates  the  subsequent  action  of  pepsin. 

Secondly,  in  connection  with  pepsin  it  causes  a  peculiar 
splitting  of  the  proteids. 

The  hydrochloric  acid  can  by  itself  split  proteids  into 
albumoses  and  peptones,  but  to  do  so  the  acid  must  be 
concentrated,  or  it  must  act  at  boiling  temperature  or  for  a 
long  time.  Pepsin  cannot  split  up  proteids  without  the  aid 
of  hydrochloric  acid. 

Perhaps  the  hydrochloric  acid  is  the  real  splitting  agent  of  the 


THE  DIGESTION  OF  THE  FOODSTUFFS  129 

gastric  juice,  while  the  function  of  the  pepsin  is  to  render  the 
proteid  capable  of  being  split  up  and  it  therefore  only  aids  the 
action  of  the  acid. 

The  action  of  the  hydrochloric  acid  is,  however,  not  a  fermenta- 
tive action,  as  is  the  case  in  the  formation  of  sugar  from  starch 
where  a  small  quantity  of  acid  can  split  an  unlimited  amount  of 
starch.  In  the  proteid  digestion,  the  acid  is  used  up,  for  it  forms 
with  the  digestion  products  the  acid  proteoses-chlor-hydrates  and 
thus  becomes  inactive.  Pepsin,  as  ferment,  is  unlimited  in  its 
action. 

Pepsin,  a  ferment  of  proteid-like  composition,  is  destroyed 

by  heating,  by  strong-  alcohol,    and   by  small  quantities   of 

free  alkali.      The  last,    however,    does   not  act  thus    in    the 

presence  of  undigested  proteid,  perhaps  because  the  pepsin 

unites  with  the  proteid. 

To  obtain  pepsin,  extract  the  mucous  membrane  of  the  stomach, 
especially  that  of  the  antrum,  with  glycerin  or  with  a  o.2f0  to  0.4$ 
hydrochloric  acid  solution. 

The  intermediate  products  thereby  formed  successively  by 
peptic  digestion  of  proteid s  are: 

1.  A  precipitate  formed  by  neutralizing  the  solution. 
Among  the  first  products  of  peptic  digestion,  especially  in 
that  of  coagulated  proteids,  there  is  present  a  proteid  coagu- 
lated by  heat,  which,  however,  soon  undergoes  a  still  further 
change. 

2.  Primary  albumoses,  protalbumose,  and  heteroalbu- 
mose,  precipitated  from  neutral  solutions  by  saturation  with 
NaCl. 

3.  A  deuteroalbumose,  which  is  precipitated  from  acid 
solutions  by  saturation  with  NaCl. 

4.  A  deuteroalbumose,  precipitated  by  saturation  with 
ammonium  sulphate. 

5.  Peptones,  not  precipitated  by  ammonium  sulphate  (see 
page  37). 

During  peptic  digestion,  not  all  the  proteid  is  completely 
changed  to  peptone ;  the  amount  of  the  resulting  peptone  is, 
e.g.  in  case  of  the  crystallized  serum  albumin  of  horse  blood, 
only  about  one-half  that  of  the  original  proteids;  the  residue 
remains  in  the  form  of  deuteroalbumose. 


130  HUMAN   PHYSIOLOGY 

The  individual  proteids,  including  those  of  vegetable 
origin,  yield  proteoses  differing  but  slightly  from  each  other. 

The  combined  proteids  are  first  split  up  by  gastric  juice 
into  their  components;  after  this,  the  proteids  thus  split  off 
are  digested  like  simple  proteids.  Nucleins  are  not  dissolved 
by  gastric  juice;  hence,  in  the  digestion  of  caseinogen,  the 
insoluble  paranuclein  remains. 

Of  the  albuminoids,  only  collagen  is  digested  by  pepsin. 
It  is  first  changed  into  its  hydrate,  gelatin,  and  from  this,- by 
hydrolytic  splitting  up,  gelatoses,  corresponding  to  proteoses, 
are  formed. 

The  process  of  proteid  digestion  by  gastric  juice  depends 
upon  : 

i.  The  amount  of  free  hydrochloric  acid,  the  amount 
most  favorable  for  digestion  being  0.2-0.4$. 

The  acidity  of  the  stomach  does  not  indicate  the  amount  of  free 
hydrochloric  acid  present  because,  first,  the  gastric  juice  may 
contain  free  organic  acids,  especially  lactic  acid,  and,  secondly, 
the  proteoses-chlor-hydrate  has  also  an  acid  reaction  (see  page  129). 
Free  hydrochloric  acid  is  present  in  the  gastric  juice  only  when  it 
gives  the  Giinzburg  reaction  (see  page  95). 

As  artificial  experiments  in  digestion  show,  the  hydrochloric 
acid  can  be  replaced  by  other  acids,  but  they  are  all  inferior  to  it. 
The  lactic  acid  frequently  formed  in  the  stomach  by  the  fermenta- 
tion of  carbohydrates  also  has  digestive  action:  it  is,  however, 
not  a  normal  constituent  of  gastric  juice  and  therefore  its  part  in 
digestion  is  only  incidental. 

2.  Upon  the  amount  of  pepsin.  The  intensity  of  the 
digestion  increases  with  the  amount  of  pepsin  present  till  it 
reaches  a  certain  limit.  The  increase  is  proportional  to  the 
square  root  of  the  concentration  of  the  pepsin. 

3.  Upon  the  kind  of  proteid  present  and  its  power  of  in- 
hibition. Fibrin,  which  is  strongly  swollen,  is  sooner 
digested  than  coagulated  white  of  egg,  which  swells  but  little. 
Native  proteids  are  more  easily  digested  than  the  coagulated, 
and  animal  proteid  more  easily  than  plant  proteid. 

4.  Upon  the  temperature.  The  gastric  juice  acts  best  at 
37-400  C.  At  oc  digestion  stops,  and  at  8o°  the  pepsin  is 
destroyed. 


THE  DIGESTION   OF   THE  FOODSTUFFS  131 

5.  Upon  the  presence  of  the  products  of  digestion.  All 
fermentation  processes  are  hindered  and  finally  arrested  by 
the  accumulation  of  the  resulting  products.  In  peptic  diges- 
tion, the  amount  of  accumulated  proteoses  must  be  very 
large  before  it  completely  stops  digestion.  This  influence 
of  the  products  of  digestion  is  not  felt  in  the  stomach  because 
the  products  formed  are  rapidly  removed. 

The  products  of  digestion  can  also  hinder  the  digestion 
by  uniting  with  the  hydrochloric  acid  and  thereby  rendering 
it  inactive.  In  this  case,  free  hydrochloric  acid  is  lacking 
and  the  addition  of  acid  starts  the  digestion  again. 

6.  Salts  can  inhibit  peptic  digestion  either  by  preventing 
the  inhibition  or  by  precipitating  the  pepsin.  This  last  is 
also  accomplished  by  alcohol  in  strong  concentration. 

Auto-digestion  of  the  stomach. — A  piece  of  the  mucosa  of  the 
stomach  heated  in  0.2$  hydrochloric  acid  at  400  C.  digests  itself. 
Why  normally  the  mucous  lining  of  the  stomach  does  not  digest 
itself  has  received  no  satisfactory  answer;  it  probably  depends 
upon  the  specific  vital  character  of  the  epithelial  cell  of  the 
mucosa. 

(b')  The  inversion  of cane-sugar . — Cane-sugar  is  inverted 
in  the  stomach,  i.e.  it  is  split  up  by  the  free  hydrochloric 
acid  into  dextrose  and  levulose. 

if)  The  coagulation  of  caseinogen. — The  caseinogen  of  the 
milk  coagulates  in  the  stomach,  previous  to  its  digestion. 
This  coagulation  is  brought  about  by  the  rennin,  which  splits 
the  caseinogen  up  into  casein  and  a  soluble  proteid  called 
whey  proteid.  Casein  unites  with  calcium,  forming  an  in- 
soluble compound,  cheese.  Hence  calcium  is  necessary  for 
the  coagulation  of  caseinogen,  and  coagulation  can  be  pre- 
vented by  precipitation  of  the  calcium  salts,  e.g.  by  oxalates. 

Rennin,  a  ferment  of  unknown  chemical  composition,  can 
act  in  an  acid,  alkaline,  or  neutral  medium. 

Rennet,  used  in  the  manufacture  of  cheese,  can  be  extracted 
from  the  stomachs  of  calves. 

As  to  the  purpose  of  milk  coagulation,  see  page  143. 

Besides  the  above-named  digestive  actions,  the  gastric 
juice  has  the  special  function  of  disinfectant.     Pathogenic  and 


132  HUMAN  PHYSIOLOGY 

putrefactive  micro-organisms,  introduced  into  the  stomach 
with  the  food,  are  killed  and  rendered  harmless  by  the 
gastric  juice.  This  action  is  especially  due  to  the  free 
hydrochloric  acid,  but  also  to  its  acid  compounds  with 
proteoses. 

Nutrition  can  go  on  normally  after  extirpation  of  the 
stomach  if  small  quantities  of  sterilized  food  are  given  at 
frequent  intervals.      This  has  been  proven  in  dogs  and  man. 

Hence  it  has  been  concluded  that  the  chief  functions  of 
the  stomach  are,  first,  to  disinfect  the  food  and,  second,  to 
serve  as  a  reservoir  for  large  quantities  of  food,  which  is 
given  out  by  the  stomach  to  the  intestine  in  such  quantities 
as  can  be  quickly  digested..  The  digestive  function  of  the 
stomach  is,  therefore,  a  secondary  affair,  seeing  that  the 
pancreatic  juice  alone  is  sufficient  for  the  digestion  of  pro- 
teids. 

3.    INTESTINAL  DIGESTION 

1 .  The  movements  of  the  intestine. — During  digestion 
the  walls  of  the  intestine  make  movements,  called  the  peri- 
staltic movements.  These  consist  of  periodic  constrictions 
of  the  intestine  brought  about  by  the  contraction  of  the  cir- 
cular muscles.  This  constriction  begins  at  the  pylorus  and 
is  propagated  to  the  rectum  in  the  form  of  a  wave.  By  these 
movements  the  chyme  is  forced  from  the  pylorus  towards 
the  rectum  and  at  the  same  time  mixed  with  the  digestive 
juices  of  the  intestine. 

Besides  the  peristaltic  movements,  the  individual  loops  of 
the  intestine  make  movements  to  and  fro,  causing  the  food 
to  be  mixed  with  the  digestive  fluids. 

The  cause  of  the  peristaltic  movements  lies  in  the  intestine 
itself,  for  an  excised  loop  of  the  intestine  moves  spon- 
taneously. If  the  intestine  is  stimulated  at  a  certain  point, 
the  contraction  begins  at  this  point  and  spreads  itself  upward 
and  downward.  The  contractions  are  perhaps  called  forth 
by  the  nervous  plexures  found  in  the  walls  of  the  intestine. 


THE  DIGESTION   OF   THE  FOODSTUFFS  133 

Moreover,  the  peristalsis  is  influenced  by  the  central 
nervous  system.  The  vagus  is  the  motor  nerve,  and  the 
splanchnic  nerve  the  inhibitory  nerve  for  the  circular  muscles. 
Stimulation  of  this  nerve  brings  about  inhibition  of  the 
peristaltic  movements. 

The  contraction  of  the  longitudinal  muscles  of  the  intestine 
produces  dilation.  The  splanchnic  is  supposed  to  be  the  motor 
nerve  for  the  longitudinal  muscles,  while  the  vagus  is  the  inhibitory 
nerve. 

2.  Chemistry  of  intestinal  digestion. — The  food,  grad- 
ually driven  from  the  stomach  into  the  intestine,  continues 
to  be  acted  upon  by  the  pepsin  as  long  as  free  hydrochloric 
acid  is  present.  But  the  free  hydrochloric  acid  is  speedily 
neutralized  by  the  alkali  of  the  secretions  which  are  poured 
upon  the  food.  There  are  three  secretions:  pancreatic  juice, 
bile,  and  intestinal  juice.  Of  these,  the  pancreatic  juice  is 
the  most  important  for  digestion. 

A.  Pancreatic  digestion.  —  The  pancreatic  juice  changes 
starch  to  sugar,  proteids  to  peptone,  and  splits  neutral  fat 
into  glycerin  and  fatty  acids.  These  actions  are  drought 
about  by  three  ferments — amylopsin,  trypsin,  and  stcapsin. 

1.  Action  of  amy  lop  sin. — Amylopsin  splits  up  starch  in 
the  same  manner  as  ptyalin  of  the  saliva.  The  starch  forms 
successively  amylo-,  erythro-,  and  achroo-dextrin,  maltose, 
and  finally  grape-sugar.  The  quantity  of  grape-sugar 
formed  is  somewhat  larger  than  that  formed  by  ptyalin,  per- 
haps because  the  pancreatic  juice  contains  more  glucase  than 
the  saliva. 

2.  Try p tic  digestion. — Trypsin  splits  up  proteid.  It  can 
act  in  an  acid  medium,  but  acts  best  in  an  alkali  medium. 
This  proteid  digestion  differs  from  peptic  digestion  in  the 
following  particulars : 

(a)  The  proteid  digestion  by  trypsin  is  carried  further  than 
that  by  pepsin.  Peptic  action  stops  at  the  formation  of 
peptones,  but  trypsin  splits  some  proteids  up  into  leucine, 
tyrosine,  and  aspartic  acid  (see  page  27).  The  peptones 
which  can  be  split  up  by  trypsin  are  called  hemipeptones ; 


134  HUMAN  PHYSIOLOGY 

those   not   capable  of  such   splitting   up  are   called   antipep- 
tones. 

(/;)  While  pepsin  digests  collagen  but  not  nuclein,  trypsin 
digests  nuclein  but  not  collagen.  Gelatin,  however,  is 
readily  digested  by  trypsin.  The  gelatin  peptones  are  not 
split  up  by  trypsin  into  amido-acids.  Elastin  is  not  digested 
by  pepsin,  but  readily  by  trypsin. 

(c)  The  products  of  proteid  digestion  by  pepsin,  injected  into 
the  blood  stream,  stop  the  coagulation  of  the  blood ;  not  so  the 
products  formed  by  tryptic  digestion. 

(</ )  The  rotatory  power  of  the  collective  products  formed  by 
peptic  digestion  is  greater  than  that  of  the  undigested  proteid, 
while  the  rotatory  power  of  the  products  of  tryptic  digestion  is 
smaller. 

(e)  In  the  presence  of  free  hydrochloric  acid,  pepsin  digests 
trypsin,  but  in  an  alkali  solution  trypsin  does  not  digest  pepsin. 

Trypsin  is  not  digested  by  pepsin  in  the  intestine,  because  the 
free  hydrochloric  acid,  in  so  far  as  it  is  not  united  with  the 
proteoses,  is  neutralized  by  the  alkali  of  the  intestinal  juices. 

During  proteid  digestion  by  trypsin  the  same  intermediate 
products  arise  as  by  peptic  digestion.  From  coagulated 
proteids  there  is  formed  in  considerable  quantities  a  soluble 
proteid,  coagulable  by  heat.  Protalbumose  and  heterc- 
albumose   are   not   formed,  but   deuteroalbumose   is  directly 

formed. 

To  obtain  trypsin  for  experimental  work,  heat  the  pan- 
creas with  highly  dilute  acetic  acid  and  extract  the  ferment 
with  glycerin.  Trypsin  is  not  found  in  the  pancreas  in  the 
form  of  active  ferment,  but  as  zymogen.  This  zymogen  is 
transformed  into  the  active  ferment  by  dilute  organic  acids. 
The  secretion  obtained  by  a  pancreatic  fistula  often  contains 
only  zymogen,  which  is  converted  into  active  trypsin  by 
coming  into  contact  with  the  acid  chyme. 

^.  Action  of  steapsin. — Steapsin  of  pancreatic  juice  is  a 
ferment  which,  by  hydrolytic  splitting  up,  changes  neutral 
fats  into  glycerin  and  free  fatty  acids.  When  alkali  carbon- 
ate is  present  in  the  intestine,  soluble  soaps  arc  formed  from 
the  fatty  acids. 

It  has   not  yet   been   determined  to  what   extent  fats   are 


THE  DIGESTION   OF   THE   FOODSTUFFS  135 

split  up.  Till  recently  it  was  maintained  that  only  a  small 
part  of  the  fat  is  split  up  and  that  the  large  residue  was 
emulsified  by  the  soap  formed  (see  page  24)  and  absorbed 
in  the  form  of  emulsion.  Recently  it  has  been  supposed 
that  all  the  fat  is  split  up  before  it  is  absorbed.  After  the 
extirpation  of  the  pancreas  the  absorption  of  fat  is  decreased. 
In  this  case,  however,  fats  are  still  split  up  by  putrefaction 
in  the  intestine.  ». 

B.  The  function  of  bile  in  the  digestion. — Bile  contains  no 
ferment,  hence  it  does  not  digest,  but  aids  i'nthe  processes 
of  digestion. 

1.  By  aiding  in  neutralizing  the  free  hydrochloric  acid. 
This  stops  the  action  of  the  pepsin  upon  the  trypsin. 

2.  By  aiding  the  action  of  pancreatic  ferments. 

3.  By  dissolving  the  free  fatty  acids. 

Besides  this,  bile  plays  an  important  part  in  the  absorption  of 
fats  (see  Chapter  X). 

Some  authors  ascribe  an  antiseptic  action  to  bile,  but  others 
deny  this. 

C.  Digestion  by  the  intestinal  juice. — Intestinal  juice  con- 
tains, besides  a  diastatic  ferment,  an  inverting  ferment  which 
changes  cane-sugar  into  dextrose  and  levulose.  Intestinal 
juice  also  splits  up  lactose,  this  not  being  absorbed  as  such. 
This  action  of  the  intestinal  juice  is  supposed  to  be  due  to 
a  ferment  called  lactase. 

The  accounts  of  other  ferments  in  the  intestinal  juice  are 
contradictory. 

The  intestinal  juice,  by  its  alkalinity,  favors  the  action  of 
the  pancreatic  ferments  and,  by  its  mucin,  favors  the  move- 
ments of  the  chyme  and  the  formation  of  faeces. 

4.    PUTREFACTION    IN    THE    INTESTINE 

In  the  intestinal  canal,  especially  in  the  lower  part  of  the 
small  intestine,  processes  of  putrefaction,  due  to  micro- 
organisms, take  place.  These  processes  change  the  con- 
tents of  the  intestine  chemically. 


136  HUMAN  PHYSIOLOGY 

The  changes  brought  about  by  the  putrefaction  are,  in 
many  respects,  similar  to  those  produced  by  digestion  ;  in 
other  respects,  they  are  very  different. 

From  proteids  there  arise  by  putrefaction  : 

1 .  Albumoses  and  peptones. 

2.  Fatty  acids,  amido-acids,  and  ammonia;  by  the  putre- 
faction of  gelatin,  glycocoll  is  also  formed. 

3.  Phenol,  paracresol,  indol,  skatol,  phenylpropionic 
acid,  phenylacetic  acid,  paraoxyphenyl-acetic  acid,  paraoxy- 
phenyl-propionic  acid. 

Indol,  CgH7N,  has  the  following  constitution  : 

c8h/ch^ch. 

b    \xh/ 


Skatol,  C9H9N: 


ch/WVh. 

\    XH    / 


Part  of  the  aromatic  products  of  proteid  putrefaction  are 
absorbed;  they  are  then  in  part  oxidized  (indol  forming  indoxyl, 
skatol  forming  skatoxyl).  The  aromatic  oxy-acids  are  not 
changed,  but  phenol,  indoxyl  and  skatoxyl  are  excreted  by  the 
urine  as  conjugated  sulphates. 

4.  Gases:  carbonic  acid,  hydrogen,  marsh  gas,  and  sul- 
phuretted hydrogen. 

Putrefaction,  therefore,  like  tryptic  digestion,  forms  pro- 
teoses and  amido-acids  from  proteids.  But  by  putrefaction 
there  are  also  formed  aromatic  decomposition  products 
(phenol,  oxy-acid,  indol,  and  skatol),  which  are  not  formed 
by  the  action  of  trypsin. 

Fats  are  split  into  fatty  acids  and  glycerin  by  putrefaction. 
The  fatty  acids  are  in  part  still  further  decomposed  into  the 
lower  fatty  acids. 

From  the  carbohydrate,  alcohol,  lactic,  acetic,  and  suc- 
cinic acids  are  formed  by  putrefaction.  Part  of  the  starch  is 
first  changed  to  sugar.  The  indigestible  cellulose  is  also 
acted  upon  by  putrefaction  ;  this,  however,  does  not  form 
sugar  but  organic  acids  (acetic,  valerianic  acid,  etc.),  car- 
bonic  acid,    and    methane.      By   this   decomposition    of   the 


THE  DIGESTION   OF   THE  FOODSTUFFS  13 7 

cellulose,  the  food   inclosed  by  it  can  be   acted   upon  by  the 

digestive  fluid. 

Concerning  the  putrefactive  decomposition  of  the  constituents 
of  the  digestive  fluids,  the  following  may  be  said:  dyslysin  is 
formed  from  cholalic  acid;  stercobilin,  the  coloring  matter  of 
faeces,  from  bile  pigments. 

5.   THE    FORMATION    OF    F.ECES    AND    THE    UTILIZA- 
TION   OF    FOODSTUFFS 

1.  Composition  of  faeces. — The  undigested,  unabsorbed 
residue  of  the  food  and  the  useless  constituents  of  the  ali- 
mentary secretion  are  called  faeces  and  are  discharged 
through  the  anus. 

The  faeces  contain : 

1.  Undigested  and  unabsorbed  constituents  of  the  food, 
such  as  remains  of  plants,  keratin,  nuclein,  muscle-fibres, 
connective  tissue,  lumps  of  casein,  starch  granules,  fat, 
haematin. 

2.  Residue  of  digestive  juices,  e.g.  cholalic  acid,  dyslysin 
formed  from  bile  acids,  bile  pigments,  cholesterin,  mucin. 

3.  Cast-off  epithelial  cells  and  their  decomposition  prod- 
ucts. 

4.  Products  of  putrefaction:  skatol,  indol,  iron  sulphide, 
fatty  acids.  Along  with  the  faeces,  the  gases  formed  by 
putrefaction  (marsh  gas,  sulphuretted  hydrogen)  are  dis- 
charged. 

5.  Mineral  matter  of  the  food  and  of  the  intestinal  secre- 
tions. 

Finally,  there  are  present  in  the  faeces  parasites  of  various 
kinds. 

The  reaction  of  the  faeces  may  be  neutral,  acid,  or  akaline. 
Its  odor  is  due  to  the  skatol,  indol,  and  other  volatile  sub- 
stances. The  color  is  generally  light  or  dark  brown ;  the 
pigment  is  the  stercobilin  produced  by  putrefaction  from 
bilirubin. 

In  the  large  intestine  the  faeces  become  solid  by  the 
absorption  of  water,  and  here  it  is  formed  into  balls. 


138  HUMAN   PHYSIOLOGY 

The  amount  of  feces  daily  discharged  is  about  120-150 
grams,  containing  30-37  grams  solids. 

2.  Utilization  of  foodstuffs. — As  the  feces  contain  un- 
digested food,  not  all  the  food  taken  into  the  alimentary 
canal  is  utilized  by  the  body.  The  amount  utilized  by  the 
body  can  be  found  by  subtracting  the  undigested  food  present 
in  the  feces  from  all  the  food  taken  by  the  mouth.  As  the 
amount  of  undigested  food  in  the  feces  has  never  been 
definitely  determined,  no  accurate  figure  of  the  amount  of 
food  absorbed  can  be  given. 

The  amount  absorbed  must  be  taken  into  consideration  in 
formulating  a  diet.  The  animal  foods  arc  better  absorbed 
than  the  vegetable  foods.      There  are  absorbed : 

I'roteid  Fat.         Carbohydrate. 

of  meat  and  eggs 97$  95$ 

"   milk    89-99$  95-97$  100$ 

"   white  bread 78%  —  99$ 

"   black  bread „  .  68-78$  89$ 

"   potatoes 68$  —  92$ 

"  turnips 61$  —  82$ 

The  reasons  why  vegetable  foods  are  so  poorly  absorbed 
are : 

(1)  The  food  in  vegetables  is  often  inclosed  in  cellulose 
membranes  which  prevent  the  action  of  digestive  juices 
upon  the  food.  Hence  vegetable  foods  are  the  better 
absorbed  in  proportion  as  they  are  free  from  the  cellulose 
membrane  in  their  preparation. 

(2)  The  cellulose  stimulates,  perhaps  mechanically,  the 
peristalsis.  Vegetable  foods  are  therefore  more  quickly 
carried  through  the  intestine  than  the  animal  foods ;  in  fact, 
so  rapidly  that  they  are  discharged  as  feces  before  they  have 
been  fully  acted  upon  and  absorbed. 

(3)  Defaecation. — The  anus  is  kept  closed  by  the  tonic 
contraction  of  the  sphincters  ani,  internus  and  externus. 
The  action  of  the  external  sphincter  is  increased  by  the 
voluntary  contraction  of  the  levator  ani,  which  is  placed  like 


THE   DIGESTION   OF   THE  FOODSTUFFS  139 

a  sling  around  the  rectum.  During  defalcation  the  tonus  of 
the  sphincters  is  inhibited,  thus  allowing  the  feces  to  pass 
•out.  The  defalcation  is  produced  by  the  peristalsis  of  the 
rectum,  aided  by  abdominal  pressure.  The  muscles  produc- 
ing this  pressure  are  the  diaphragm  and  the  muscles  of  the 
abdominal  walls. 

The  centre  of  defalcation  is  situated  in  the  lumbar  cord. 
It  is  stimulated  reflex ly  from  the  rectum.  The  inauguration 
of  the  reflex  depends,  to  a  certain  extent,  upon  the  will. 
The  nerves  going  from  the  centre  to  the  muscles  of  the 
rectum  run  through  the  hypogastric  plexus  and  the  sympa- 
thetic (ganglion  mesentericum  posticus)  and  the  nervi 
erigentes.  The  first-named  nerves  are  supposed  to  be  motor 
nerves  for  the  circular  muscles  and  inhibitory  nerves  for  the 
longitudinal  muscles ;  the  last-named  are  supposed  to  be 
motor  nerves  for  the  longitudinal  muscles  and  inhibitory 
nerves  for  the  circular  muscles. 

Defalcation  takes  place  in  man  at  least  once  a  day. 


CHAPTER    X 

ABSORPTION    AND    ASSIMILATION    OF    FOODSTUFFS 

1.      GENERAL     REMARKS     ABOUT     ABSORPTION     AND 
ASSIMILATION 

UNDER  absorption  we  include  the  processes  whereby  the 
dissolved  foodstuffs  and  the  emulsified  fats  are  taken  up  from 
the  mucous  lining  of  the  stomach  and  intestine  and  are 
brought  directly  or  by  means  of  the  lymphatics  into  the 
blood,  by  which  they  are  carried  to  the  organs  and  tissues 
of  the  body. 

By  assimilation  we  understand  the  processes  which  the 
absorbed  foodstuffs  undergo  till  as  constituents  of  the  cells 
and  tissues  they  are  consumed  in  the  activity  of  the  tissues. 

As  the  insoluble  and  undialyzable  food  is  rendered  soluble 
and  dialyzable  by  digestion,  it  is  probable  that  osmosis 
of  the  soluble  substance  plays  an  important  part  in  absorp- 
tion. Still  there  are  certain  facts  about  absorption  which 
cannot  be  explained  by  the  laws  of  osmosis  as  known  to  us 
at  present.  Absorption  often  takes  place  contrary  to  the 
laws  of  osmosis.  On  the  one  hand,  water  is  absorbed  from 
a  sodium  chloride  solution  placed  in  the  intestine  even  though 
of  higher  osmotic  pressure  than  the  blood,  whereas,  accord- 
ing to  the  laws  of  osmosis,  water  ought  to  pass  from  the 
blood  or  lymph  into  the  intestine.  On  the  other  hand, 
undialyzable  substances,  like  proteid  and  emulsified  fat,  are 
taken  from  the  intestine  by  the  blood. 

The  force  which    causes  this   absorption   contrary  to  the 

140 


ABSORPTION  AND   ASSIMILATION   OF  FOODSTUFFS       141 

laws  of  osmosis  is  due  to  the  activity  of  the  epithelial  cells. 
This  view  is  supported  by  the  fact  that  when  the  intestinal 
epithelial  cells  are  rendered  functionless  by  sodium  fluoride 
(which  does  not  destroy  the  cells  anatomically),  absorption 
follows  the  law  of  osmosis. 

The  seat  of  absorption  is  chiefly  the  intestine ;  in  a  less 
degree,  the  stomach.  Pure  water  is  not  absorbed  from  the 
stomach ;  on  the  contrary,  water  is  passed  by  the  mucous 
lining  into  the  stomach.  Aqueous  solutions  of  salts,  sugar, 
and  peptones  are  absorbed  when  they  are  very  concentrated. 
Absorption  from  the  stomach  is  favored  by  table-salt  and 
spices,  such  as  mustard,  peppermint,  pepper.  Alcohol  and 
other  narcotics  also  favor  absorption  because  they  paralyze 
the  resistance  which  the  epithelium  of  the  stomach  offers  to 
the  absorption  of  foodstuffs. 

Most  of  the  absorption  takes  place  in  the  small  intestine, 
where  the  surface  for  absorption  is  very  large.  The  villi  of 
the  mucous  membrane  of  the  intestine  increase  the  absorp- 
tion surface  to  twenty-three  times  what  it  would  be  if  no 
villi  were  present.  One  sq.  cm.  of  the  intestinal  mucosa 
contains  about  2500  villi. 

The  epithelial  cells  of  the  intestinal  mucosa  are  cylindri- 
cal. The  free  surface  of  these  cells  is  striated.  Each  villus 
•contains  a  central  lacteal,  and  between  this  lacteal  and  the 
■outside  border  of  the  villus  are  the  blood  vessels,  a  mass  of 
capillaries,  and  the  afferent  and  efferent  vessels.  The  lac- 
teal is  surrounded  by  smooth  muscle-fibres,  by  the  contrac- 
tion of  which  the  villi  are  shortened,  the  lacteal  is  pressed 
together,  and  the  contents  emptied  into  the  lymph  vessels. 

In  the  large  intestine  also  considerable  absorption  takes 
place.  Among  other  things  water  is  here  absorbed  whereby 
the  contents  of  the  intestine  become  more  solid.  Food  is 
also  absorbed  in  the  large  intestine  when,  in  soluble  form, 
it  is .  forced  through  the  anus  into  the  intestine  as  nutritive 
clyster. 

The  path  of  the  absorbed  food  from  the  intestine  is  two- 
fold:   (1)  The  portal  vein;    (2)  the  lymph  vessels.  • 


142  HUMAN   PHYSIOLOGY 

Water,  salts,  si/gar,  and  protcids  arc  absorbed  by  the 
portal  vein;  fats  arc  absorbed  by  the  lymphatics.  After  the 
water,  salts,  and  sugar  have  traversed  the  epithelial  layer, 
the}'  pass  into  the  closely  adjoining"  blood  capillaries. 
Thence  they  are  carried  with  the  blood  through  the  portal 
vein.  When  great  quantities  of  fluids  have  been  taken,  a 
part  may  reach  the  lymph  vessels.  It  has  been  observed  in 
animals  that  the  lymph  in  the  thoracic  duct  is  increased 
only  when  a  large  quantity  of  water  is  imbibed,  and  that  the 
carbohydrates  in  the  lymph  are  increased  on])-  during  the 
absorption  of  a  large  quantity  of  concentrated  sugar  solution. 
The  blood  of  the  portal  vein,  however,  always  contains, 
during  absorption  of  carbohydrates,  more  sugar  than  arterial 
blood.  Observations  upon  human  beings  with  thoracic  duct 
fistula,  from  which  all  the  lymph  from  the  intestine  flows, 
show  that  the  lymph  contains  at  best  only  traces  of  the 
absorbed  sugar. 

That  the  absorbed  proteids  are  carried  through  the  portal 
vein  is  proven  by  the  facts  that  ligaturing  the  thoracic  duct 
does  not  interfere  with  the  proteid  nutrition  and  metabolism, 
and  that  the  lymph  flowing  from  a  thoracic  duct  fistula,  as 
mentioned  above,  shows  no  increase  of  proteids  during  their 
absorption. 

Fats,  on  the  other  hand,  are  mostly  absorbed  by  the 
lacteals.  During  the  absorption  of  fats  the  lacteals  and  the 
thoracic  duct  appear  white,  because  of  the  milky  turbulence 
due  to  the  absorbed  emulsified  fat.  But  as  all  the  fat  eaten 
cannot  be  demonstrated  in  the  lymph  flowing  from  the 
thoracic  duct  or  from  a  chylus  fistula  during  the  absorption 
of  fat,  it  has  been  assumed  that  part  of  the  fat  is  absorbed 
by  the  blood  vessels. 

2.   ABSORPTION    AND    ASSIMILATION    OF    PROTEIDS 

Before  proteoses  are  absorbed  into  the  blood,  they  undergo 
a  change  in  the  wall  of  the  intestine.  The  blood  of  the 
portal  vein  and  the  lymph  contain  no  proteoses.     If  proteoses 


ABSORPTION  AND  ASSIMILATION   OF  FOODSTUFFS       J 43 

are  injected  into  the  blood,  they  arc  rapidly  excreted  by  the 
kidneys. 

The  change  from  proteoses  to  simple  proteids  takes  place 
in  the  epithelial  cells  of  the  intestine,  for  the  native  proteids 
of  the  body  are  increased  when  no  other  proteids  than  pro- 
teoses are  given  in  the  food.  Hence  the  real  body  proteid 
must  have  been  formed  from  the  proteoses  of  the  food. 

If  a  solution  of  proteoses  is  heated  at  body  temperature  with 
the  fresh  mucous  lining  of  the  intestine,  the  proteoses  gradually 
disappear  without  the  further  formation  of  decomposition  products. 
This  supports  the  view  that  the  proteoses  are  changed  back  to 
native  proteids. 

Solutions  of  native  proteids,  acid  and  alkali  albumin  can 
also  be  absorbed  as  such  without  previous  digestion.  It  has 
been  observed  that  such  proteids,  placed  in  an  isolated  loop 
of  intestine  free  from  ferment,  are  rapidly  and  completely 
absorbed  without  albumoses  and  peptones  having  been 
formed.  These  proteids,  injected  into  the  blood  are 
assimilated  and  used  by  the  body;  this,  however,  is  not  true 
of  caseinogen,  egg  albumin,  and  haemoglobin,  for  they  are 
rapidly  excreted  by  the  kidneys  if  injected  into  the  blood. 

Large  quantities  of  egg  albumin  solution  taken  into  the 
stomach  can  also  be  absorbed  without  previous  digestion, 
but  are  then  excreted  by  the  kidneys.  Caseinogen  and 
haemoglobin  are  precipitated  in  the  stomach  and  are  there- 
fore not  absorbed  without  digestion  and  the  transformation 
into  new  proteid  in  the  intestinal  wall.  This  perhaps  ex- 
plains the  meaning  of  the  caseinogen  coagulation  by  rennin, 
for,  if  the  caseinogen  was  not  precipitated,  it  might  be 
absorbed  as  such  and  then  be  excreted  by  the  kidneys. 

Many  soluble  proteids  can,  therefore,  be  absorbed  and 
assimilated  and  used  in  the  body  without  being  digested  or 
changed;  others,  on  the  contrary,  must  first  be  digested. 
The  object  of  digestion  is  therefore,  first,  to  render  insoluble 
proteids  soluble  and,  secondly,  to  change  the  proteids  which 
are  soluble  but  cannot  be  assimilated  to  proteids  which  can 
be  assimilated. 


144  HUMAN  PHYSIOLOGY 

Proteids  which  are  soluble  and  can  be  assimilated  are, 
without  doubt,  also  digested,  but  the  extent  of  this  digestion 
cannot  be  stated.  The  digestion  of  proteids  capable  of 
assimilation  is,  however,  of  real  significance,  since  their  rate 
of  absorption  is  thus  increased. 

Absorbed  proteids  reach  the  blood,  most  likely,  chiefly  in 
the  form  of  albumin,  as  the  quantity  of  serum  albumin  of  the 
blood  is  increased  by  the  eating  of  proteids. 

Concerning  the  further  history  of  proteids  and  assimilation 
nothing  is  known. 

3.   ABSORPTION    AND    ASSIMILATION    OF    FATS 

From  the  fatty  acids  or  soaps  and  glycerin  formed  by  the 
splitting  up  of  fats  during  digestion,  neutral  fats  are  again 
formed  in  the  mucosa  of  the  intestines.  Even  if  fatty  acids 
or  soaps  arc  eaten,  neutral  fat  is  present  in  the  lymph;  in 
this  case  the  glycerin  necessary  for  the  formation  of  neutral 
fats  must  have  been  formed  in  the  intestinal  wall  itself.  If 
a  mixture  of  soap  and  glycerin  is  heated  with  the  intestinal 
mucous  membrane,  neutral  fats  are  also  formed.  This  forma- 
tion of  neutral  fats  takes  place  in  the  epithelial  cells.  During 
the  digestion  of  fats  the  epithelial  cells  of  the  intestine  are 
filled  with  fat  droplets  of  various  sizes. 

But  the  fat  found  in  the  epithelial  cells  is  not  necessarily 
derived  from  the  union  of  the  fatty  acid  and  glycerin  taking 
place  in  these  cells;  for  neutral  fats  in  the  emulsified  state 
may  be  taken  up  by  them  directly. 

The  opinion  is  current  that  most  of  the  fat  is  absorbed  in 
the  emulsified  condition,  and  that  only  such  a  quantity  of  fat 
is  split  up  as  is  necessary  to  furnish  the  fatty  acids  or  soap 
needed  for  this  emulsification.  But  the  correctness  of  this 
view  is  doubtful  because  the  other  necessary  condition  for 
emulsification — the  alkaline  reaction  of  the  contents  of  the 
intestine — is  frequently  wanting.  The  contents  of  most  of 
the  upper  part  of  the  small  intestine  have  an  acid  reaction 
due  to  free  fatty  acids  ;   yet  here  fats  are  also  absorbed,  as  is 


ABSORPTION  AND   ASSIMILATION   OF  FOODSTUFFS       145 

shown  by  the  milky  contents  of  the  lacteals.  Hence  it  is 
difficult  to  decide  in  how  far  the  splitting  up  and  emulsifica- 
tion  of  fats  take  place. 

The  absorption  of  emulsified  fat  is  supposed  to  be  brought 
about  by  the  active  movements  of  the  striated  border  of  the 
epithelial  cells. 

The  absorption  of  fats  is  aided  by  the  bile.  Animals  with 
a  biliary  fistula  absorb  but  little  of  the  fat  eaten.  This  favor- 
able action  of  bile  is  supposed  to  be  due  to  the  fact  that  it 
dissolves  free  fatty  acids  and  the  insoluble  calcium  and  mag- 
nesium soaps,  and  that  the  striated  border  of  the  epithelial 
cells  is,  by  the  bile,  rendered  permeable  for  the  emulsified 
fat.  Both  these  actions  are  attributed  to  the  bile  salts. 
The  soda  of  the  bile  also  aids  in  the  emulsification  of  fats. 

If,  by  pancreatic  extirpation,  the  steaptic  digestion  is  pre- 
vented, the  amount  of  fat  absorbed  is  greatly  reduced. 
This,  however,  is  not  true  for  the  fat  of  milk,  for  this  is 
already  in  a  finely  emulsified  condition. 

From  the  epithelial  cells  the  emulsified  fat  is  transferred 
to  the  lymph  and  with  this  is  carried  through  the  thoracic 
duct  into  the  blood.  The  fat,  in  so  far  as  it  is  not  directly 
oxidized,  is  stored  up  in  the  cells  of  the  adipose  tissues  of 
the  body. 

The  amount  of  fat  in  the  blood  is  somewhat  greater  during 
fat  absorption  than  during  fasting.  During  starvation  the 
amount  of  fat  in  the  blood  is  also  increased,  for  then  the  fat 
stored  up  in  the  tissues  is  transported  by  the  blood  to  the 
place  of  combustion. 

Immediately  after  a  meal  rich  in  fat,  large  quantities  of 
fat  appear  in  the  liver  cells  (physiological  filtration  of  fat), 
which  disappear  after  a  short  time. 

4.     ABSORPTION    AND    ASSIMILATION    OF    CARBO- 
HYDRATES 

The  monosaccharides  are  carried 'by  the  portal  vein  to  the 
liver  without  having  undergone  any  change  in  the  walls  of 
the  intestine. 


146  HUMAN  PHYSIOLOGY 

Cane-sugar  and  lactose  are  generally  not  absorbed  as  such,  but 
are  split  up  into  their  simple  sugars.  Only  when  they  are  taken 
in  very  large  quantities  are  they  absorbed  as  such  into  the  blood, 
but  are  then  excreted  by  the  kidneys. 

In  the  liver,  the  monosaccharides  are  changed  to  glycogen 
and  stored  up  in  this  form  (see  page  23).  The  object  of 
this  glycogen  formation  is  to  prevent  the  sugar  from  too 
great  accumulation  in  the  blood  ;  for  if  the  percentage  of 
sugar  in  the  blood  rises  above  a  certain  limit  (0.2$),  the 
excess  is  excreted  by  the  kidneys. 

The  per  cent  of  sugar  in  the  portal  vein  during  absorption 
of  carbohydrates  is  greater  than  that  in  arterial  blood  or  in 
blood  from  the  hepatic  vein. 

Glycogen  can  be  formed  from  dextrose,  levulose,  and 
galactose.  The  glycogen  formed  from  levulose  and  galactose 
is  identical  with  that  formed  from  dextrose.  When  glycogen 
is  formed  from  levulose  and  galactose,  they  are  first  changed 
to  dextrose,  for  in  the  splitting  up  of  glycogen  only  dextrose 
results. 

The  amount  of  glycogen  in  the  liver  depends  upon  the 
nutrition  and  upon  the  amount  of  material  used  up  by  the 
body.  After  a  long  fast  and'  also  after  severe  muscular  work 
and  strong  cooling  of  the  body,  the  liver  is  free  from  gly- 
cogen. After  a  meal  rich  in  carbohydrates  the  liver  of  a 
rabbit  contains  as  much  as  \yi  glycogen.  In  the  liver  of  a 
criminal  executed  shortly  after  a  meal,  6%  glycogen  was 
found.  A  liver  free  from  glycogen  is  small  and  has  a  dark 
brown  color,  while  the  liver  rich  in  glycogen  is  large  and 
has  an  ochre  color.  A  liver  rich  in  glycogen  may  weigh 
three  times  as  heavy  as  one  poor  in  glycogen  ;  this  is  not 
only  due  to  the  larger  amount  of  glycogen,  but  also  to  the 
large  amount  of  other  solids  and  of  water  present. 

The  glycogen  is  stored  up  in  the  cells  in  the  form  of  flakes.  It 
can  be  obtained  from  the  liver  by  cutting  the  liver  into  small  pieces 
and  boiling  in  water  to  which  a  little  acetic  acid  has  been  added. 
By  this  the  proteids  are  coagulated  and  the  glycogen  is  dissolved, 
forming  an  opalescent  solution  from  which  it  may  be  precipitated 
by  alcohol. 


ABSORPTION  AND   ASSIMILATION   OF  FOODSTUFFS       147 

When  needed,  the  glycogen  in  the  liver  is  again  trans- 
formed into  dextrose  which  is  carried  out  by  the  venous 
blood  to  the  tissues.  At  this  time  the  per  cent  of  sugar  in 
the  blood  of  the  hepatic  vein  is  greater  than  that  in  the 
arterial  blood  or  blood  from  the  portal  vein.  Both  the  for- 
mation of  glycogen  and  its  reconversion  into  sugar  are 
brought  about  by  the  liver  cells. 

Carbohydrates  in  the  form  of  glycogen  are  also  stored  up 
in  the  muscles,  and  are  used  up  when  needed,  e.g.  during 
muscular  activity.  The  muscle-glycogen  is  supposed  not  to 
be  identical  with  that  formed  in  the  liver.  At  all  events  the 
glycogen  of  the  muscles  is  not  derived  as  such  from  the 
liver. 

When  the  carbohydrates  in  the  food  are  present  in  excess, 
the  bod\-,  by  reduction  and  synthesis,  forms  fat  from  them 
and  thus  stores  them  up. 

In  diabetes  mellitus  the  glycogenic  function  of  the  liver 
is  disturbed.  This  causes  sugar  to  accumulate  in  the  blood 
to  such  an  extent  that  it  is  excreted  by  the  kidneys.  We 
can  discriminate  between  two  forms  of  diabetes,  a  mild  form, 
in  which  sugar  appears  in  the  urine  only  when  carbohydrates 
are  eaten,  and  a  severe  form,  in  which  sugar  is  excreted  even 
if  no  carbohydrates  are  eaten.  In  the  latter  case  the  sugar 
is  derived  from  the  proteids.  Nothing  is  positively  known 
concerning  the  immediate  cause  of  diabetes.  Artificial 
diabetes  may  be  produced : 

1 .  By  the  so-called  diabetic  puncture  ;  Piqure)  whereby  a 
part  of  the  medulla  at  the  lower  end  of  the  calamus  scrip- 
torius  is  destroyed.  This  seems  to  prove  that  the  glycogenic 
function  of  the- liver  is  dependent  upon  the  central  nervous 
system. 

2.  By  extirpation  of  the  pancreas  (see  Chapter  XI). 

3.  By  various  poisons:  phloridzin,  curare,  phosphorus, 
corrosive  sublimate. 

The  amido-acids  (leucine,  tyrosin,  etc.)  formed  from  the  hemi- 
peptones  by  pancreatic  digestion  are  also  absorbed,  and  in  the  liver 
thev  are  changed  to  urea. 


148  HUMAN   PHYSIOLOGY 

The  products  of  putrefaction,  phenol,  aromatic  oxy-acids,  indol 
and  skatol  are  also  ahsorbed  in  part,  but  are  excreted  by  the 
kidneys  (see  pages  51,    104  and   136). 

Besides  the  products  of  digestion  of  foods,  some  of  the  con- 
stituents of  the  digestive  fluids  are  absorbed,  e.g.  the  bile 
salts,  which,  arriving  at  the  liver,  stimulate  the  bile  secre- 
tion. The  digestive  ferments,  pepsin  and  ptyalin,  when 
absorbed,  are  excreted  by  the  kidneys,  while  trypsin  and 
steapsin  are  destroyed  in  the  blood. 

According  to  another  view,  the  ferments  excreted  by  the 
kidneys  are  not  derived  from  the  intestine,  but  are  absorbed, 
in  the  form  of  zymogens,  by  the  blood  from  the  glands 
between  the  periods  of  digestive  activity. 

Other  mucous  membranes,  besides  those  of  the  stomach 
and  intestine,  are  able  to  absorb  dissolved  substances,  but 
such  absorption  is  of  no  physiological  importance. 

The  skin  can  absorb  small  quantities  of  certain  substances. 

Subcutaneous  injection  of  foodstuffs. — Many  foods  can 
be  used  by  the  animal  economy  when,  in  proper  form,  they 
are  directly  introduced  into  the  tissue  fluids.  This  is  true  in 
case  of  subcutaneous  injection  of  native  albumin,  fat,  or 
dextrose. 


CHAPTER    XI 

THE  CHANGES  OF  BLOOD  IN  THE  ORGANS.    INTERNAL 

SECRETION 

From  what  has  been  said  in  the  foregoing  chapters,  it 
follows  that  the  blood  streaming  through  an  organ  is  changed 
not  only  in  respect  to  its  gases  but  that  it  must  undergo 
other  changes  as  well.  In  the  organs  in  which  the  physio- 
logical combustion  takes  place,  e.g.  in  the  muscles,  the 
blood  supplies  the  material  for  this  combustion  and  acquires, 
besides  the  carbon  dioxide,  other  products  of  combustion, 
especially  those  containing  nitrogen.  In  the  glands  the 
blood  loses  substances  from  which  the  secretions  are  formed ; 
in  the  walls  of  the  intestine  it  takes  up  the  absorbed  foods ; 
in  the  liver  and  in  the  adipose  tissue  it  either  deposits  the 
carbohydrates  and  fats  or,  if  necessary,  takes  them  up. 
Moreover,  the  blood  as  a  tissue  (see  page  52)  has  its  own 
metabolism,  by  which  it  is  chemically  changed.  The  above- 
mentioned  changes  in  the  blood  have,  in  some  cases,  been 
demonstrated.  But  in  most  cases  a  difference  cannot  be 
detected,  because  the  amount  of  the  substance  given  up  or 
acquired  by  the  blood  in  flowing  through  an  organ  is  so 
small  in  proportion  to  the  amount  of  blood  flowing  to  and 
from  that  organ  that  it  lies  within  the  limits  of  error  of 
observation. 

Besides  the  changes  in  the  blood  which  we  can  under- 
stand from  the  known  physiological  properties  of  the  organ, 
it  undergoes  still  other  changes,  concerning  the  nature  and 
significance  of  which  very  little  is  known.  Many  organs 
appear   either  to   alter   deleterious    substances  found   in   the 

149 


150  HUMAN  PHYSIOLOGY 

blood,  by  changing  them  into  harmless  products,  or  by 
forming  and  giving  up  to  the  body  substances  which  influence 
either  the  metabolism  or  act  upon  the  nervous  or  muscular 
system.  This  process  is  called  "internal  secretion,"  since 
these  organs  throw  their  products  into  the  blood. 

Among  the  organs  which  have  an  internal  secretion  are 
all  the  blood  glands,  the  thyroid  and  suprarenal  glands,  the 
liver,  the  pancreas,  and  perhaps  the  testes. 

Among  the  blood  glands  are  also  classed  the  spleen  and  thymus 
gland,  whose  function  is  not  so  much  a  secretion  as  the  formation 
and  destruction  of  blood  corpuscles  (see  pages  88  and  89). 

I.  The  thyroid  gland. — The  thyroid  gland  contains  in  its 
connective  tissue  many  completely  closed-  vesicles.  The 
walls  of  these  vesicles  are  formed  by  a  single  layer  of 
cuboidal  cells  and  the  vesicles  are  filled  with  a  "  colloid  " 
substance.  The  thyroid  gland  must  be  regarded  as  a  true 
ductless  gland,  the  cuboidal  cells  being  the  secreting  gland- 
cells;  the  colloidal  contents  of  the  vesicles,  the  secretion. 
The  contents  of  the  vesicles  are  emptied  into  the  lymph 
spaces  between  the  vesicles  and  are  thus  carried  to  the 
blood. 

After  the  thyroid  gland  has  been  excised  for  goitre,  a 
series  of  severe  disturbances  has  been  observed  which  sooner 
or  later  end  in  death  (cachexia  strumipriva).  Diseases  of 
the  nervous  system  (diminution  of  psychical  functions, 
idiocy,  and  motor  and  sensory  paralysis  or  spasms),  degen- 
eration of  the  liver  and  kidneys,  disturbances  in  metabolism 
and  in  the  regulation  of  body  heat  set  in.  These  phenomena 
are  also  present  during  disease  of  the  thyroid  gland,  when 
cedamentous  swelling  of  the  skin  and  idiocy  are  especially 
marked  (myxcedema).  In  dogs,  extirpation  of  the  thyroid 
gland  produces  death  in  a  few  days,  preceded  by  strong 
spasms  and  severe  disturbance  in  nutrition.  In  rabbits, 
extirpation  of  the  thyroid  is  generally  not  fatal,  but  leads  to 
changes  in  metabolism,  myxoedemous  swelling  of  the  skin, 
scaly  eruptions,  and  shedding  of  the. hair. 

The  injurious  effects  of  extirpation  or  disease  do  not  appear 


INTERNAL   SECRETIONS  151 

when  a  small  part  of  the  gland  is  retained  or  when  the 
thyroid  gland  is  transplanted  to  the  peritoneal  cavity  or  when 
fresh  or  dried  thyroid  glands  are  given  by  mouth.  The 
abnormal  enlargement  of  the  thyroid  (goitre)  can  also  be 
relieved  by  feeding  on  thyroid  glands. 

One  of  the  most  striking  effects  of  the  therapeutical  use  of 
thyroid  preparation  is  the  rapid  fall  in  body  weight  and  the 
disappearance  of  body  fat.  This  loss  of  weight  is  due,  as 
has  been  shown  by  experiments  in  metabolism,  partly  to 
the  withdrawal  of  water  from  the  tissues,  the  water  in  the 
urine  being  increased,  and  parti}-  by  the  not  inconsiderable 
increase  in  combustion.  By  feeding  a  rabbit  sufficiently  with 
thyroid  glands,  the  combustion  processes  can  be  doubled. 
The  combustion  of  proteid,  is,  however,  little  affected  as 
long  as  non-nitrogenous  material,  especially  fat,  is  present. 

The  thyroid  gland  is  therefore  indispensable  for  life. 
Most  likely  its  importance  lies  in  the  fact  that  it  produces 
one  or  more  substances  which  are  absolutely  essential  for  the 
normal  course  of  life's  processes.  An  excess  of  these  sub- 
stances produces  severe  disturbances  in  the  nervous  system 
and  metabolism,  and  can  also  produce  death.  From  the 
thyroid  gland  there  has  been  isolated  a  substance  containing 
iodine,  thyroiodin,  which  is  believed  to  be  the  active  principle 
of  the  gland,  for  iodine  has  a  certain  therapeutical  action 
upon  hypertrophic  thyroid  glands.  But,  as  all  thyroid  glands 
do  not  contain  this  substance,  and  as  thyroiodin  does  not 
show  all  the  actions  of  the  thyroid  gland,  we  can  hardly 
regard  it  as  the  active  substance. 

The  thymus  is  supposed  to  have  the  same  function  as  the 
thyroid  gland,  for  feeding  on  thymus  is  said  to  have  the  same 
result  as  feeding  on  thyroid  glands. 

II.  Suprarenal  capsules. — The  suprarenal  capsules  con- 
sist of  cellular  parenchyma  surrounded  by  connective  tissue 
capsules.  The  parenchyma  forms  a  clear  cortical  and  a  dark 
red  medullary  portion.  In  both  the  cortical  and  the  medul- 
lary portion  numerous  nerve  elements  (non-medullated  nerve 
fibres,  sympathetic   ganglionic  cells)   are  present.      Because 


152  HUMAN   PHYSIOLOGY 

of  this  abundance  of  nerve  elements,  the  suprarenal  capsules 
have  been  regarded  as  nervous  organs  for  the  inhibition  of 
peristaltic  movements  of  the  intestine. 

As  extirpation  of  the  suprarenal  capsules  results  in  a  gen- 
eral paralysis  and  finally  death,  the}-  must  be  regarded  as 
vital  organs.  The  injection  of  an  aqueous  extract  of  supra- 
renal capsule  is  said  to  remove  the  effects  of  extirpation. 
This  aqueous  extract  contains  two  substances,  whose  chemi- 
cal nature  is  not  yet  known.  Of  these  the  one  causes  a 
considerable  increase  in  blood  pressure,  while  the  other  can 
decrease  the  pressure  but  works  more  feebly  than  the  first. 
This  increase  in  blood  pressure  caused  by  the  first-mentioned 
substance  is  due  to  a  general  contraction  of  the  small 
arteries.  The  anatomical  part  upon  which  this  substance 
acts  lies  in  the  walls  of  the  blood  vessel  itself.  It  paralyzes 
the  central  nervous  system.  It  stimulates  not  only  the 
muscles  of  the  blood  vessels  but  also  the  skeletal  muscles; 
hence  its  function  seems  to  be  to  increase  the  tonus  of  the 
muscles,  both  of  the  skeletal  and  of  the  blood  vessels. 

Concerning  the  manner  in  which  the  second  substance 
acts  nothing  certain  has  yet  been  determined. 

Pathological  changes  in  the  suprarenal  capsules  are  followed 
by  an  abnormal  coloring,  bronzing,  of  the  skin  (which  is  also  said 
to  follow  the  extirpation  of  the  suprarenal  capsule).  This  is  called 
Addison's  disease. 

The  active  substances  of  the  suprarenal  capsule  extract  are 
rendered  inert  by  passing  them  through  the  liver. 

III.    The  liver. — Besides  functioning  in  the 
(i)  Secretion  of  bile  (see  page  99), 

(2 )  formation  of  glycogen  (see  page  146),  and 

(3)  breaking  up  and  formation  of  red  blood   corpuscles 

(pages  54  and  100), 

the  liver  also  has  the  important  function  of 

(4)  changing  the  ammonia   salts,  produced  by  proteid 

metabolism,  into  urea  (in  mammals)  or  into  uric 
acid  (in  birds  and  reptiles).  (See  pages  45  and 
47-) 


INTERNAL    SECRETIONS  153 

If  the  liver  is  isolated  from  the  circulation  by  joining  the 
portal  vein  directly  with  the  inferior  vena  cava,  the  urine 
excreted  contains  less  urea  and  more  ammonium  salts  than 
normally  and  the  animal  shows  symptoms  of  poisoning- 
characteristic  of  the  ammonium  compounds.  Extirpation 
of  the  liver  in  birds  is  followed  by  the  appearance  of 
ammonia  and  lactic  acid  in  the  urine  instead  of  uric  acid. 

The  object  of  this  change  which  the  ammonia  salts 
undergo  in  the  liver  seems  to  be  to  change  the  poisonous 
ammonia  into  harmless  substance. 

The  liver,  inserted  as  a  filter  between  the  capillary  network  of 
the  portal  vein,  acts  upon  the  substances  absorbed  from  the  intes- 
tine. In  the  first  place,  it  changes  the  injurious  products  of 
proteid  putrefaction,  phenol,  skatol,  indol,  into  the  harmless 
ethereal  sulphates  which  are  excreted  in  the  form  of  alkali  salts. 
In  the  second  place,  the  liver  retains  the  vegetable  and  animal 
poisons  (alkaloids)  incidentally  introduced  into  the  alimentary 
canal;  these  poisons  are  destroyed  and  excreted  with  the  bile.  In 
the  third  place,  metallic  poisons  (arsenic,  antimony,  lead)  are 
deposited  in  the  liver  and  the  body  is  thus  shielded  from  their 
injurious  effect.      These  poisons  are  also  finally  excreted. 

The  anatomical  relation  between  the  spleen  and  the  liver  (the 
splenic  vein  is  a  branch  of  the  portal  vein)  points  to  a  physiological 
relation  between  these  two  organs.  Perhaps  the  haemoglobin  set 
free  in  the  spleen  by  the  breaking  down  of  the  red  blood  corpus- 
cles is  decomposed  in  the  liver. 

In  the  rabbit  many  lobes  of  the  liver  can  be  removed  without 
any  disturbance  being  noticed.  The  extirpated  lobes  are  soon 
replaced. 

IV.  The  pancreas. — Besides  the  secreting  of  pancreatic 
juice,  the  pancreas  plays  an  important  part  in  the  metabolism 
of  carbohydrates.  After  extirpation  of  the  pancreas  the 
carbohydrates  are  no  longer  properly  oxidized  in  the  body 
and  hence  are  largely  excreted  with  the  urine  (pancreatic 
diabetes).  If  a  small  part  of  the  pancreas  is  left,  no  diabetes 
results.  On  the  other  hand,  injection  of  pancreatic  juice  or 
feeding  with  pancreas  does  not  stop  the  diabetes,  but  in- 
creases it.  Extirpation  of  the  pancreas  causes  the  liver  to 
lose  its  power  of  forming  glycogen,  and  the  tissues  their 
power  of  oxidizing  sugar. 


154  HUMAN  PHYSIOLOGY 

V .  The  testes. — In  addition  to  their  function  as  repro- 
ductive organs,  the  testes  stand  in  close  connection  with  the 
whole  body.  This  connection  is,  no  doubt,  brought  about 
by  substances  furnished  by  the  glands  to  the  blood,  which 
modify  the  vital  processes.  Extirpation  of  the  testes  (castra- 
tion) in  a  boy  is  folio  wed  by  disturbances  in  development. 
The  voice  does  not  change  at  puberty,  the  muscles  remain 
soft,  and  there  is  no  development  of  manly  strength  and 
character.  Also  in  adult  man,  castration,  or  premature 
atrophy  of  the  testes,  is  followed  by  disturbances  in  the 
nervous  system  and  psychical  life.  It  is  said  that  subcu- 
taneous injection  of  testes-extract  increases  manly  strength 
and  thereby  increases  the  bodily  and  psychical  well-being. 
Nothing  is  known  concerning  the  nature  of  the  active  sub- 
stance. 

Functions  of  a  similar  nature  to  those  of  the  above-described 
organs  have  been  attributed  to  the  ovaries,  prostate,  hypophyses, 
and  kidneys,  but  nothing  certain  is  known  about  them. 


CHAPTER    XII 

METABOLISM 

While  we  have  thus  far  considered  the  individual  sub- 
stances taken  up  and  cast  out  by  our  body  and  have 
explained  their  importance,  we  shall  now  treat  of  the 
balance,  or  the  comparative  composition  of  the  quantities  of 
the  substances  taken  up  and  cast  out  by  the  body  collec- 
tively. This  balance  not  only  gives  us  the  extent  of  meta- 
bolism, but  also  shows  us  the  relation  and  the  use  of  each 
foodstuff  to  the  animal  economy.  At  the  same  time  we  can 
thereby  learn  how  a  person  can  best  support  himself  with 
the  most  appropriate  food  at  the  least  expense  and  how  to 
bring  his  body  to  a  desired  state  of  nutrition.  Upon  the 
results  of  this  balance  of  metabolism  is  based  the  practical 
science  of  dietetics. 

1.    METHODS   OF   INVESTIGATION    IN    METABOLISM 

To  strike  a  balance  of  nutrition,  we  must  know  the  quan- 
tity taken  up  and  given  off. 

The  substances  taken  up  are  food  and  the  inhaled  oxygen. 

The  substances  cast  out  of  the  body  are  found  in  the 
urine,  faeces,  sweat,  expired  air;  smaller  amounts  in  the 
sebum  of  the  skin,  in  the  cast-off  horny  epithelium,  hairs, 
nails,  at  times  in  the  menstrual  blood,  milk,  and  semen. 
Of  these,  as  a  rule,  only  those  present  in  the  urine,  faeces, 
and  expired  air  are  taken  into  account  in  the  balance  of 
nutrition.      The  others  are  present  in   such   small  quantities 

155 


156  HUMAN  PHYSIOLOGY 

that  they  do  not  need  to  be  considered  or  are  excluded  by 
the  condition  of  the  experiment. 

The  ideal  experiment  in  metabolism  would  be  to  estimate 
quantitatively  each  individual  constituent  of  the  incomings 
and  outgoings  and  to  use  the  results  in  striking  the  balance 
of  nutrition.  But  this  is  impossible  because  of  unavoidable 
difficulties  in  the  methods  of  investigation.  Hut  to  form  a 
correct  conception  of  the  extent  and  nature  of  the  metabol- 
ism, it  is  sufficient  to  know  the  amount  of  some  of  the  con- 
stituents or  even  some  of  the  elements  of  the  income  and 
outgo.  Of  these  elements  the  most  important  are  the 
carbon,  nitrogen,  the  oxygen  of  inhaled  air,  and  frequently 
the  sulphur  and  phosphorus. 

The  nitrogen  both  of  the  income  and  outgo  can  be 
directly  determined  by  Kjeldahl's  method,  by  which  the 
nitrogen  of  the  substance  to  be  analyzed  is  changed,  by 
boiling  with  concentrated  sulphuric  acid  and  mercury,  into 
ammonia,  and  as  such  it  may  be  measured. 

The  carbon  of  the  income  and  of  the  urine  and  feces  is 
determined  by  analysis.  The  expired  carbon  is  calculated 
from  the  amount  of  carbon  dioxide  exhaled. 

The  inhaled  oxygen  is  either  determined  directly  from  the 
amount  of  oxygen  taken  from  the  respired  air  or  calculated 
from  the  other  data  of  the  balance  of  nutrition. 

The  taking  up  of  oxygen  and  the  giving  off  of  carbon 
dioxide  is  called  "respiratory  metabolism." 

For  investigating  the  respiratory  metabolism,  we  may  use 
the  apparatus  of:  (1)  Pettenkofer-Voit,  (2)  Regnault-Reiset, 
or  (3)  Geppert-Zuntz. 

By  the  Pettenkofer  -  Voit  apparatus  the  gaseous  outgo  of 
carbon  dioxide  and  water  vapor  is  determined  directly.  This  is 
done  as  follows:  A  person  breathes  in  a  hermetically  sealed 
chamber.  The  percentage  of  carbon  dioxide  and  water  vapor  of 
the  air  inhaled  is  known,  and  the  amount  of  respiration  is  measured 
by  a  gasometer.  The  increase  in  carbon  dioxide  and  water  vapor 
in  the  expired  air  is  determined  by  taking  an  accurately  measured 
quantity  of  air  from  the  chamber  and  passing  it  through  a  weighed 
quantity  of  .sulphuric  acid  and  through  potassium  hydrate,  the  one 


METABOLISM  157 

retaining  the  water,  the  other  the  carbon  dioxide.  From  the 
increase  in  weight  of  the  sulphuric  acid  and  potassium  hydrate, 
the  amount  of  water  and  carbon  dioxide  given  off  by  the  person 
can  be  calculated. 

The  inhaled  oxygen  can  be  found  indirectly  as  follows:  The 
sum  total  of  the  income  (food  -f-  oxygen)  and  the  body  weight  at 
the  beginning  of  the  experiment  must  be  equal  to  the  sum  of  the 
outgoings  and  the  body  weight  at  the  end  of  the  experiment. 
Hence 

Oxygen  =  (final  weight  -f-  outgoings)  —  (initial  weight  -\-  food). 

For  this  calculation  the  weight  of  the  urine,  fasces,  and  food, 
and  also  that  of  the  body  at  the  beginning  and  at  the  end  of  the 
experiment,  must  be  determined. 

In  the  respiratory  apparatus  of  Regnault  and  Reiset,  the  inhaled 
oxygen  is  measured  directly.  It  consists  of  an  air-tight  chamber, 
which  is  supplied  from  the  outside  with  pure  oxygen  only,  while 
the  carbon  dioxide  formed  is  absorbed  by  the  potassium  hydrate. 
This  causes  a  decrease  in  the  volume  of  gas  in  the  chamber,  and 
hence  new  quantities  of  oxygen  are  forced  into  the  chamber. 
The  volume  of  oxygen  used  is  thus  determined,  while  the  potas 
sium  hydrate  holds  all  the  carbon  dioxide. 

While  the  calculation  of  the  respiratory  metabolism  in  the  above- 
described  methods  includes  the  gas-exchange  of  the  skin,  by  the 
method  of  Geppert  and  Zuntz  the  gas-exchange  of  the  lungs  only 
is  determined.  In  this,  the  experimenter  does  not  breathe  in  a 
closed  chamber,  but,  the  nose  being  closed,  he  breathes  through 
a  closed  mouthpiece  which  is  connected  with  the  so-called 
Miiller's  valves  which  separate  the  inspired  from  the  expired  air. 

By  this  method  also,  the  oxygen  taken  up  and  the  carbon 
dioxide  given  off  is  determined  directly,  for,  in  measured  quanti- 
ties of  inspired  and  expired  air,  the  oxygen  and  carbon  dioxide  are 
determined  by  gas  analysis.  As  the  amount  of  air  inhaled  and 
exhaled  is  measured  by  a  gasometer,  the  total  amount  of  oxygen 
taken  up  and  of  carbon  dioxide  given  off  can  be  calculated. 

Occasionally  it  may  be  of  interest  to  know  the  changes  in 
the  sulphur,  phosphorus,  and  the  salts.  The  sulphur  and 
phosphorus  of  the  income  are  changed  to  sulphuric  acid 
and  phosphoric  acid  by  oxidation,  and,  as  such,  they  are 
estimated.  In  the  same  way  the  sulphur  and  phosphorus 
of  the  faeces  may  be  determined.  In  the  urine  the  sulphur 
and  phosphorus  are  already  oxidized  to  sulphuric  acid  and 
phosphoric  acid. 


158  HUM AN  PHYSIOLOGY 

The  salts  of  the  income  and  outgo  are  determined  in  the 
ash. 

The    water   is    generally   accounted   for    as    such    in    the 
balance  of  nutrition. 

To  be  of  an\r  value  in  judging  the  metabolism  of  the  body, 
the  experiments  on   metabolism   must   be  carried  on  for  an 
extended  period.      Unless  otherwise  indicated,  the  results  of 
such  experiments  are  calculated  upon  a  basis  of  twenty-four 
hours. 


2.   THE    VALUE   OF  THE    RESULTS    OF    EXPERIMENTS 
IN    METABOLISM 

Determination  of  the  carbon  furnishes  the  basis  for  study- 
ing the  history  of  all  the  organic  foodstuffs  in  the  body.  If 
carbon  equilibrium  is  obtained,  i.e.  if  as  much  carbon  is 
taken  up  as  is  given  off,  as  great  a  quantity  of  organic  sub- 
stances is  consumed  in  the  body  as  is  taken  up.  If  more 
carbon  is  taken  up  than  is  given  off,  the  body  stores  up 
organic  substances;  but  if  more  is  given  off  than  is  taken  up, 
the  body  loses  some  of  its  organic  constituents. 

Determination  of  the  nitrogen  affords  us  information  as  to 
the  proteids  in  the  body,  for  all  the  nitrogen  of  the  income 
is  contained  in  the  proteid.  As  the  proteids  contain  on  the 
average  16$  nitrogen,  the  amount  of  nitrogen  found,  multi- 
plied by  6.25,  gives  the  corresponding  amount  of  proteid. 
If  the  amount  of  proteid  decomposed  in  the  body  is  equiva- 
lent to  that  taken  up,  the  body  is  in  nitrogenous  equilib- 
rium. If  more  nitrogen  is  taken  up  than  is  given  off,  flesh 
is  formed.  But  if  the  body  gives  off  more  nitrogen  than  it 
takes  up,  it  loses  some  of  its  proteids. 

The  proportion  of  the  nitrogen  to  the  carbon  in  the  pro- 
teids is  as  I  :  3.3.  From  the  estimated  nitrogen  of  the  in- 
come and  outgo,  it  can  be  calculated,  by  means  of  these 
figures,  how  much  of  the  carbon  of  the  income  and  outgo 
is  derived  from  proteids.  If  the  amount  of  carbon  derived 
from  the  proteid   is    subtracted  from  the   whole   quantity  of 


METABOLISM  159 

carbon  in  the  income  and  outgo,  the  remainder  will  indi- 
cate the  amount  of  carbon  derived  from  the  non-nitrogenous 
fat  and  carbohydrates.  We  can  thus  determine  how  much 
non-nitrogenous  foodstuff  is  consumed  in  the  body  and 
whether  the  body  has  increased  or  decreased  in  non-nitro- 
genous substances. 

Determination  of  the  inhaled  oxygen  is  of  importance  in 
understanding  the  metabolic  processes,  for  in  warm-blooded 
animals  the  amount  of  inhaled  oxygen  is  a  measure  of  the 
extent  of  combustion  taking  place  in  the  body.  From  the 
amount  of  oxygen  consumed,  it  can  also  be  calculated  how 
much  hydrogen,  besides  the  carbon,  is  oxidized  in  the  body. 

In  cold-blooded  animals  the  estimation  of  oxygen  is  of  little 
value,  as  the  oxygen  inhaled  is  not  directly  used  up,  but  is  stored 
up  for  a  longer  or  shorter  time,  because  these  animals  can  live  for 
some  time  in  an  atmosphere  free  of  oxygen.  Warm-blooded 
animals,  on  the  contrary,  do  not  store  up  oxygen  to  any  great 
extent  and  can  therefore  endure  the  lack  of  oxygen  for  but  a  few 
minutes.  An  exception  to  this  are  the  warm-blooded  hibernating 
animals,  which  appear  to  be  able  to  store  up,  during  the  period  of 
activity,  a  considerable  amount  of  oxygen. 

The  respiratory  quotient,  or  the  proportion  between  the 
volumes  of  the  carbon  dioxide  exhaled  and  oxygen  inhaled, 
tells  us  how  much  of  the  inhaled  oxygen  is  used  to  oxidize 
carbon,  forming  the  carbon  dioxide  exhaled  by  the  lungs, 
and  how  much  of  it  is  used  in  oxidizing  other  elements, 
especially  hydrogen. 

When  pure  carbon  is  oxidized  to  carbon  dioxide,  the  resulting 
carbon  dioxide  has  the  same  volume  as  the  oxygen  consumed. 
In  such  a  case  the  respiratory  quotient  is  one.  But  if,  in  addition 
to  carbon,  hydrogen  is  also  oxidized,  then  the  resulting  volume 
of  carbon  dioxide  is  less  than  the  oxygen  used  up,  and  the  more 
hydrogen  is  oxidized,  the  less  is  the  volume  of  carbon  dioxide. 
In  such  a  case  the  respiratory  quotient  is  less  than  one. 

The  value  of  the  respiratory  quotient  with  carbohydrate 
combustion  is  1;  with  proteid  combustion,  0.8;  with  fat 
combustion,  0.7. 

Carbohydrates    contain     sufficient    oxygen    to    oxidize    all    the 


160  HUMAN  PHYSIOLOGY 

hydrogen,  hence  all  the  inhaled  oxygen  is  used  in  the  oxidation 
of  the  carbon.  One  litre  of  oxygen  used  furnishes  i  litre  of 
carbon  dioxide.  Proteids  and  fats  do  not  contain  sufficient  oxygen 
to  oxidize  all  their  hydrogen.  If  i  litre  of  oxygen  is  used  to 
oxidize  proteids.  800  cc  of  carbon  dioxide  are  formed;  if  used  to 
oxidize  fats,  only  700  cc  are  formed. 

The  respirator}-  quotient  can  also  be  greater  than  one 
when  the  amount  of  carbon  dioxide  is  greater  than  that  of 
the  oxygen  taken  up.  This  is  the  case  when,  in  the  body, 
substances  rich  in  oxygen,  e.g.  carbohydrates,  are  reduced 
to  products  containing  less  oxygen,  e.g.  fats. 

The  respirator}'  quotient  can  also  be  less  than  it  is  during 
oxidation  of  pure  fat.  This  occurs  when  the  oxygen  intro- 
duced is  stored  up  in  the  form  of  compounds  rich  in  oxygen. 

The  respiratory  quotient  is  therefore  subject  to  consider- 
able variations.  It  is  greatest  during  a  carbohydrate  diet, 
smallest  during  a  fat  diet.  But  independently  of  the  diet, 
the  respiratory  quotient  has  been  observed  to  undergo 
periodic  variations,  for  sometimes  relatively  more  carbon 
dioxide  is  given  off;  at  another  time  relatively  more  oxygen 
is  taken  up.  This  shows  that  the  oxygen  taken  up  is  not 
immediately  used  for  the  formation  of  carbon  dioxide,  but 
first  forms  compounds  rich  in  oxygen  which  are,  at  a  later 
time,  completely  oxidized  to  carbon  dioxide  and  water. 

Determining  the  amount  of  the  sulphur  and  phosphorus 
in  the  income  and  outgo  is  also  of  value  in  studying  the 
proteid  metabolism. 

The  balance  of  water  shows  not  only  how  much  water  has 
been  taken  up  and  given  off  by  the  body,  but  also  how  much 
water  has  been  formed  by  combustion  processes  in  the  bod}-. 

In  regard  to  the  substances  excreted  in  the  faxes,  it  must 
still  be  mentioned  that  the  faxes  contain  not  only  end- 
products  of  metabolism,  but  also  undigested  and  unabsorbed 
parts  of  the  food.  The  quantity  of  the  latter  substances 
must  be  subtracted  from  the  food  taken  up,  for  the  foodstuffs 
not  absorbed  cannot  be  included  in  the  metabolism.  But  we 
have  not  yet  been  able  to  separate  the  end-products  of  meta- 
bolism  present    in    the   faeces  from    the    merely  unabsorbed 


METABOLISM  161 

iood.  The  amount  of  the  nitrogen  in  the  end-products  of 
metabolism  present  in  the  faeces  of  an  adult  man  is  estimated 
at  one  gram  per  day.  This  figure  is  based  on  observations 
made  upon  the  faeces  during  inanition. 

3.   EXAMPLE    OF    A    BALANCE    OF    NUTRITION 

To  illustrate  the  balance  of  nutrition  we  will  assume  the 
following  case :  A  man  whose  body  weight  at  beginning  of 
experiment  is  70  kg  remains  for  twenty-four  hours  in  the 
chamber  of  Voit's  respiratory  apparatus.  He  is  fed  with 
meat,  bread,  butter,  potatoes,  table-salt,  and  water.  During 
this  time  his  body  weight  increases  to  70.138  kg. 

1 .  The  amount  of  food  taken  up  is  (in  grams) : 

Proteids ,  130  containing    69  C,  21  N 

Fat 100  "  76   •• 

Carbohydrates 400  ••  176   " 

Salts 30 

Water 2100 

Total  income 2760  containing  321  C,  21  N 

2.  The  amount  of  the  outgo  in  urine,  faeces,  and  respira- 
tion is  (in  grams) : 

Urine.  . 1355  containing  1280  H20,  24  salts,  12  C,  18  N 

F:eces 120         "  85     "  6     "  18   "  3" 

Respiration 1867  "  950     ''  250   " 

Total  outgo  ....   3342  containing  2315  H20,  30  salts,        280  C,  21  X 

The  person  has  therefore  given  off  3342  g,  while  the  income  is 
2760  g.  The  body  weight  increased  during  this  time  138  g. 
Hence  some  other  substance  must  have  been  taken  in  beside  the 
food,  and  this  is  the  inhaled  oxygen. 

3.  The  amount  of  this  oxygen  can  be  calculated  from  the 
above  data  according  to  the  following  formula : 

Oxygen  =  (final  body  weight  +  outgoings)  —  (initial  body  weight  -4-  food) 
=  (70138  +  3342)    "     —  (70000  +  276o)g 

=  720  g. 

4.  From  the  foregoing  we  can  strike  the  following  balance 
of  nutrition  (in  grams): 


162  Hi' MAN  PHYSIOLOGY 

Income   (food  -f-  oxygen) 34&o  containing     321  C,  21  N,  30  salts 

Outgo 3342         "  280'-  21"  30     •• 

]  litt'erence + 1 3^  +41  C 

This  table  teaches  us  the  following-  facts : 

1.  The  person  was  in  nitrogenous  equilibrium,  for  the 
nitrogen  of  the  outgo  equals  the  nitrogen  taken  in  with 
the  proteids  of  the  food. 

2.  The  person  was  not  in  carbon  equilibrium,  for  the  out- 
go contains  41  g  carbon  less  than  the  income.  These  41  g 
carbon  have  been  stored  up  in  the  bod}-. 

From  the  figures  of  the  nitrogen  it  can  be  calculated  that 
69  g  carbon  originated  from  the  ingested  and  decomposed 
proteid.  Of  the  321  g  carbon  ingested  and  of  the  280  g 
carbon  going  out,  69  g  originated  from  the  proteid,  hence 
252  g  carbon  in  the  form  of  non-nitrogenous  food  has  been 
ingested.  Of  this,  211  g  [280  —  69]  was  given  off,  hence 
41  Ar  of  carbon  in  the  form  of  a  non-nitrogenous  substance  is 
stored  up  in  the  body. 

3.  Whether  this  41  g  carbon  is  stored  up  in  the  form  of 
fat  or  carbohydrate  can  be  determined  from  the  value  of  the 
respirator}*  quotient.  The  volume  of  the  exhaled  carbon 
dioxide  amounts  to  464  litres ;  the  volume  of  the  consumed 
oxygen  is  503  litres.  This  would  give  us  the  value  of  the 
respirator}'  quotient : 

_   ^         vol.  CO.,        464 

R.O.  =  — -p-i-  =  4  4  =  0.92. 

^  vol.  02         503 

This  respirator}' quotient  is  less  than  one,  i.e.  some  of  the 
oxygen  inhaled  has  been  used  to  oxidize  hydrogen.  It  is, 
however,  much  larger  than  that  of  proteid,  which  is  to  say, 
that,  beside  the  proteid,  but  little  fat  and  much  carbohydrate 
has  been  consumed. 

The  following  may  still  be  said  concerning  the  respiratory 
quotient.  By  calculation  it  will  be  found  that  53  g  of  the  inhaled 
oxygen  have  been  used  up,  not  in  the  oxidation  of  carbon,  but  in 
the  formation  of  water.  The  hydrogen  necessary  for  this  has  been 
derived  from  proteids  and  fats — not  from  carbohydrates,  for  they 
contain  sufficient  oxygen  to  unite  with  all  the  hvdrogen. 


METABOLISM  163 

Of  the  proteids  of  the  food  about  116  g  have  been  consumed. 
From  the  hydrogen  and  oxygen  found  in  this  quantity  must  be 
subtracted,  first,  the  amount  found  in  the  urea  and,  secondly,  the 
amount  of  hydrogen  which  can  be  oxidized  by  the  oxygen  present 
in  the  proteid.  This  leaves  3.  5  g  hydrogen,  which  need  for  their 
oxidation  28  g  of  the  inhaled  oxygen. 

Of  the  fat  of  the  food  about  90  g  have  been  absorbed.  For  the 
oxidation  of  the  hydrogen  found  in  it,  75.  5  g  of  the  inhaled  oxygen 
are  needed.  But  of  the  inhaled  oxygen  there  are  remaining  only 
(53  —  28)  =  25  g.  Hence  only  30  g  of  fat  can  have  been  oxi- 
dized ;  the  remaining  60  g  have  been  deposited  in  the  body.  60  g 
fat  contain  45  g  carbon,  which  corresponds  quite  closely  with  that 
found  in  the  experiment  (41  g). 

Hence  carbon  in  the  form  of  fat  must  have  been  retained 
in  the  body,  while  the  carbon  of  carbohydrates  has  been 
entirely  oxidized. 

4.  There  have,  then,  been  deposited  in  the  body  41  g  of 
carbon  or  about  55  g  of  fat.  But  the  total  increase  in  body 
weight  was  138  g,  hence  83  g  more.  These  83  g  can  be 
present  in  the  body  only  as  water.  The  balance-sheet  of 
the  water  shows  that  2100  g  were  taken  up  and  2315  g 
given  off,  hence  more  water  has  been  given  off  than  taken 
up.  But  it  must  be  remembered  that  in  the  oxidations 
taking  place  in  the  body,  water  has  been  formed.  From 
the  oxidized  carbohydrates  222  g  and  from  the  proteid  48  g 
and  from  the  fat  30  g  of  water  have  been  formed,  making  a 
total  of  300  g.  Of  this,  215  g  [2315  — 2 100]  have  been 
excreted,  while  the  remaining  85  g  remain  in  the  body. 
This  agrees  quite  well  with  the  observed  figure. 

5.  The  balance-sheet  of  the  salts  shows  that  as  much  salt 
has  been  given  off  as  taken  up.  Hence  the  body  has  neither 
increased  nor  decreased  in  salt. 

4.    METABOLISM    UNDER    VARIOUS    CONDITIONS 

The  extent  of  metabolism  is  influenced  by: 

(1)  The  amount  and  composition  of  the  food; 

(2)  The  work  done  and  heat  lost  by  the  organism ; 

(3)  The  size  of  the  body,  age,  and  sex. 
I.  Influence  of  food  upon  metabolism. 


1 64  HUMAN  PHYSIOLOGY 

A.   Metabolism  of  the  resting  body  during  inanition. — 

For  a  full  understanding  of  the  metabolic  processes  in  the 
body  it  is  of  great  importance  to  know  the  extent  of  meta- 
bolism going  on  during  hunger  when  the  body  receives  no 
food  or  only  part  of  the  necessary  food.  In  such  a  case,  the 
animal  maintains  the  processes  of  combustion  more  or  less 
at  the  expense  of  its  own  body  substance. 

The  inanition  may  either  be  complete,  no  food  being  taken 
in  at  all,  or  partial  when  only  one  kind  of  foodstuff  is  taken, 
or  when  all  the  necessary  kinds  are  taken  but  in  insufficient 
quantities. 

(a)  Absolute  inanition. — Even  though  no  food  is  taken 
at  all,  still  the  processes  of  combustion  go  on,  although 
somewhat  reduced.  But  not  all  the  factors  of  the  total 
metabolism  are  equally  influenced.  The  giving  off  of  in- 
organic constituents,  water  and  salts,  steadily  decreases 
during  the  hunger  period.  The  excretion  of  sodium  chloride 
soon  ceases  altogether,  while  of  the  other  salts,  especially 
potassium  and  calcium  phosphates,  small  quantities  are 
excreted  even  up  to  the  time  of  death,  for  these  salts  are 
rendered  unnecessary  by  the  continual  breaking  down  of  the 
tissues.  Shortly  before  death,  the  amounts  of  water  and 
salts  excreted  are  increased ;  this  corresponds  to  the  in- 
creased breaking  down  of  the  tissue  immediately  prior  to 
death. 

The  carbon  dioxide  decreases  most  during  the  first  stages 
of  starvation ;  during  the  latter  part  it  is  but  slightly 
decreased.  It  is  difficult  to  obtain  accurate  figures  as  to 
this,  for  the  extent  of  the  decrease  in  the  carbon  dioxide 
excretion  is  dependent  upon  the  quantity  and  nature  of  food 
eaten  shortly  before  the  beginning  of  starvation. 

The  oxygen  taken  up  is  also  decreased  during  starvation, 
but  not  to  such  an  extent  as  the  carbon  dioxide  excretion. 
Hence  the  decrease  in  the  extent  of  the  combustion  during 
starvation  compared  with  that  of  a  well-fed  animal  is  not 
as  great  as  the  decrease  in  the  formation  of  the  carbon 
dioxide.      During  starvation  less  carbon  but  more  hydrogen 


METABOLISM  165 

is  oxidized,  so  that  the  oxygen  consumption  is  decreased  at 
most  by  20-25$.  Hence  the  respiratory  quotient  during  the 
first  days  of  fasting  is  rapidly  decreased,  but  after  this 
remains  quite  constant  till  a  few  days  before  death.  The 
more  body  fat  there  is  present,  the  smaller  the  value  of  this 
constant  respiratory  quotient.  In  animals  well  provided 
with  fat,  the  respiratory  quotient  has  a  value  which  it  ought 
to  have  when  pure  fats  are  oxidized.  A  few  days  before 
death  by .  starvation  the  respiratory  quotient  is  increased 
because  of  the  increased  proteid  consumption. 

The  amount  of  proteid  consumed  (the  nitrogen  excretion) 
decreases  very  rapidly  to  less  than  one-half  and  then  remains 
constant  for  a  few  days  till  a  little  while  before  death,  when 
it  becomes  larger  than  it  was  before  starvation.  The  course 
of  proteid  consumption  during  starvation  depends  upon  the 
amount  of  non-nitrogenous  material  for  combustion  stored 
up  in  the  body.  Of  this  material  the  fats  only  are  of  impor- 
tance, since  the  carbohydrates  (glycogen)  are  already  used 
up  in  the  first  days  of  starvation.  The  longer  the  supply  of 
fat  lasts,  the  longer  it  takes  before  the  excretion  of  nitrogen 
is  increased. 

That  the  excretion  of  nitrogen  reaches  its  minimum  during 
the  first  days  of  starvation,  that  it  then  remains  constant  for 
some  time,  and  at  last  again  increases,  is  evidently  due  to 
the  fact  that,  at  first,  less  proteids  are  used  in  the  process  of 
combustion  than  fats,  and  during  the  latter  part  more. 

The  amount  of  material  lost  is  not  the  same  for  all  organs. 
The  organs  and  tissues  suffering  most  are  the  adipose  tissue, 
the  muscles,  and  the  abdominal  glands;  the  heart,  brain, 
and  muscles  of  respiration  suffer  less.  During  inanition  the 
body  loses  continually  in  weight,  this  loss  being  greatest 
during  the  first  days.  Of  this  loss,  two  thirds  is  due  to  loss 
in  water,  one  third  to  loss  in  body  proteid  and  fat.  The 
amount  of  fat  lost  is  from  two  to  four  times  that  of  the  pro- 
teids lost. 

The  time  when  death  occurs  is  therefore  dependent  upon 
the  condition  of  the  body  nutrition  at  the  beginning  of  star- 


166  HUMAN  PHYSIOLOGY 

vation.      Death   occurs  when   a  little  more   than  one-half  of 
the  bod}'  weight  has  been  lost. 

Besides  the  loss  of  material,  starvation  causes  the  following 
results:  The  activity  of  the  heart  decreases,  the  number  of  beats 
is  lessened.  General  weakness  sets  in  (psychical  depression). 
The  body  temperature  remains  the  same  except  just  before  death, 
when  it  falls  considerably.  The  indol  and  aromatic  oxyacids  of 
the  urine  formed  by  putrefaction  in  the  intestine  disappear,  but 
phenyl  sulphuric  acid  is  excreted  with  the  urine  till  death  sets  in. 

(b)  Partial  inanition. — \(  only  some  constituents  of  food 
necessary  for  life  are  given,  or  if  all  the  constituents  are 
given  but  in  insufficient  quantities,  death  by  starvation  is  but 
delayed. 

1.  Lack  of water  in  the  food  causes  death  more  speedily 
than  lack  of  all  food.  This  is  evidently  due  to  the  fact  that, 
for  the  normal  course  of  metabolism,  a  definite  proportion 
must  exist  between  the  water  and  the  solid  constituents  of 
the  bod)-.  Besides  this,  dry  food  is  very  soon  refused,  so 
that  lack  of  water  is  finally  followed  by  absolute   starvation. 

2.  Salt-hunger. — If  no  salts  are  present  in  the  food,  the 
excretion  of  salts  steadily  decreases  and  the  excretion  of 
sodium  chloride  soon  ceases  altogether  even  at  a  time  when 
the  bod\"  still  contains  considerable  quantities  of  it.  Potas- 
sium and  calcium  phosphates  are,  however,  continually 
excreted.  By  eating  organic  foods  the  excretion  of  calcium 
phosphate  is  somewhat  decreased,  because  the  salt,  derived 
from  the  breaking  down  of  the  tissue,  can  be  utilized  in  the 
regeneration  of  the  tissues.  Still  a  part  of  the  salts  is  con- 
tinually lost,  and  since,  for  the  maintenance  of  life,  a  certain 
proportion  must  exist  between  the  salts  and  the  organic 
constituents  of  the  bod}-,  death  finally  sets  in.  Death  is 
preceded  by  weakness  and  paralysis. 

3.  Lack  of  all  organic  constituents  in  the  food. — If  no 
organic  foodstuffs  are  given,  the  animal  being  supplied  only 
with  water  and  salts,  death  by  starvation  occurs.  The 
phenomena  of  metabolism  are  practically  the  same  as  in 
absolute    inanition,    the    organism    consumes    its   own   body 


METABOLISM  I     " 

substance.       Death,   however,    occurs  a    little   later   than    in 
complete  starvation. 

4.  Lack  of  proteids. — If  proteids  are  excluded  from  the 
food,  while  sufficient  water,  salts,  carbohydrates,  and  fats 
are  given,  the  body  loses  its  proteids,  and  since  the  fats  and 
carbohydrates  cannot  shield  it  against  the  loss,  death  by 
starvation  results.  The  daily  loss  of  proteid  is,  however, 
slightly  less  than  in  absolute  hunger,  and  hence  death  occurs 
somewhat  later  and  without  the  previous  increase  in  nitrogen 
excretion. 

Notwithstanding  the  loss  of  body  proteids,  the  body  can 
lay  up  fat  if  the  food  contains  sufficient  quantities  of  fats  and 
carbohydrates. 

Even  the  taking  up  of  gelatin  cannot  prevent  the  loss  of 
body  proteids.  But  the  loss  of  body  proteid  is  less  if 
gelatin  is  eaten  than  if  nothing  but  fats  and  carbohydrates 
are  taken.  Proteoses,  however,  are  able  to  replace  all  the 
proteids  used  in  the  body. 

5.  Lack  of  fats  and  carbohydrates  in  the  food  while  suffi- 
cient proteids  are  fed. — Fats  and  carbohydrates  can  be  com- 
pletely replaced  by  proteids,  at  least  in  the  carnivorous 
animals.  For  example,  by  feeding  upon  lean  meat,  which 
is  nearly  a  pure  proteid  diet,  a  dog  can  maintain  life.  But 
it  is  not  possible  to  feed  man  for  a  long  time  exclusively 
with  proteid,  as  he  cannot  digest  the  necessary  amount  of 
meat. 

6.  If  all  the  necessary  foods  are  given  but  in  insufficient 
amounts,  two  cases  are  possible,  (i;  The  quantity  is  abso- 
lutely insufficient.  The  body  now  continually  uses  some  of 
its  own  constituents,  hence  death  by  starvation  must  finally 
set  in,  but  at  a  much  later  time  than  in  absolute  starvation. 
(2)  The  quantity  of  food  given  is  only  relatively  insufficient 
to  maintain  the  body  at  the  beginning  of  starvation.  In  this 
case,  the  body  loses  some  of  its  substance  until  the  amount 
used  and  the  amount  taken  are  equal.  Then  the  body 
maintains  itself.  Hence  the  body  emaciates,  but  death  does 
not  result. 


1 68  HUMAN  PHYSIOLOGY 

B.  Metabolism  during  sufficient  nutrition. — The  partak- 
ing of  food  increases  the  metabolism  as  compared  with  that 
during  inanition.  In  this  respect  the  animal  body  is  not 
like  a  furnace  in  which  increase  of  consumption  follows  in- 
crease of  supply,  for  the  body  can  store  up  a  considerable 
amount  of  material  for  combustion.  Besides  this,  the  increase 
in  metabolism  is  less  dependent  upon  the  absolute  quantity 
of  material  furnished  than  upon  the  composition  of  the 
material. 

i.  The  effect  of  proteid  upon  metabolism. — The  effect  of 
proteid  upon  metabolism  can  best  be  investigated  in  the 
carnivorous  animals,  which  can  maintain  life  if  merely  pro- 
teids  are  given  in  the  food  in  addition  to  salts  and  water. 
Suppose  a  dog  is  fed  with  as  much  proteid  as  it  consumes. 
Its  body  will  be  in  nitrogenous  equilibrium,  for  the  nitro- 
genous income  and  outgo  are  balanced.  If  to  such  a  dog 
more  proteids  are  fed,  the  larger  part  is  used,  while  only  a 
small  part  is  stored  up  in  the  body  as  flesh. 

By  this  laying  up  of  flesh  the  demand  for  proteid  is  in- 
creased, for  the  demand  is  proportional  to  the  weight  of  the 
body  flesh.  Nitrogenous  equilibrium  is  again  obtained, 
when  the  proteids  demanded  by  this  newly  laid  up  flesh 
equal  the  increase  in  the  quantity  of  the  food  proteids.  But 
the  possibility  of  such  storing  up  of  flesh  is  limited,  for  the 
digestive  organs  cannot  cope  with  very  large  quantities  of 
proteids. 

If  a  dog,  maintained  in  nitrogenous  equilibrium  by  proteids 
only,  receive  less  proteids,  the  body  loses  some  of  its  flesh 
till  the  amount  of  body  proteid  has  reached  the  point  where 
the  demand  upon  proteid  is  equal  to  the  proteids  supplied  in 
the  food ;  nitrogenous  equilibrium  is  then  once  more  estab- 
lished. At  a  certain  low  limit  of  proteid  supply,  nitrogenous 
equilibrium  is  not  regained,  for  then  the  bod}'  continually 
uses  more  proteid  than  is  supplied,  and  hence  death  by 
starvation  must  result. 

The  smallest  amount  of  proteid  with  which  an  animal 
living  upon   a    pure   proteid  diet   can    maintain    nitrogenous 


METABOLISM  169 

equilibrium  is  considerably  more  than  the  amount  of  proteid 
decomposed  during  starvation.  If  an  animal  takes  up  just 
as  much  proteid  as  it  decomposes  during  starvation,  nitroge- 
nous equilibrium  is  not  obtained,  but  the  animal  decomposes, 
in  addition  to  the  food  proteid,  some  of  its  bod}'  proteid. 
The  more  proteid  is  given  in  its  food,  the  less  body  proteid 
will  be  used,  and  when  about  two  and  one  half  times  as 
much  proteid  is  fed  as  is  decomposed  during  starvation, 
nitrogenous  equilibrium  is  obtained. 

The  facts  derived  from  the  study  of  metabolism  during 
pure  proteid  feeding  establish  the  following  laws : 

1.  Within  certain  limits  the  bod}' can  maintain  nitroge- 
nous equilibrium  with  any  amount  of  food  proteid. 

2.  Increase  in  food  proteid  also  increases  the  consumption 
of  proteids. 

This  increase  in  proteid  consumption  has  been  regarded  as 
"  Luxus-consumption,  but  it  is  not  without  beneficial  effect,  for 
bv  it  the  power  of  the  body  is  increased. 

2.  Effect  of  fats  and  carbohydrates  on  metabolism. — If  a 
person  fed  on  a  mixed  diet  (proteid,  fats,  carbohydrates, 
water,  and  salts)  and  brought  to  a  condition  of  nutritive 
equilibrium  is  supplied  with  an  increased  amount  of  non- 
nitrogenous  foods  (fats  and  carbohydrates),  the  amount  of 
non-nitrogenous  material  consumed  in  the  bod}'  is  increased, 
but  the  consumption  of  proteids  is  decreased  to  an  extent 
expressed  by  the  law  of  isodynamics  (see  page  117). 
Hence,  in  reality,  no  general  increase  of  combustion  in  the 
body  will  take  place.  Fats  and  carbohydrates  therefore 
shield  the  proteids,  and  the  proteid  is  stored  up  in  the.  body 
as  flesh.  If  there  is  still  more  fat  or  carbohydrate  present 
in  the  food,  these  are  stored  up  in  the  bod}',  chief!}'  in  the 
form  of  fat. 

As  far  as  their  influence  upon  the  extent  of  metabolism  is 
concerned,  there  is  no  real  difference  between  fats  and  carbo- 
hydrates, but  the  carbohydrates  are  more  easily  oxidized  and 
shield  the  proteids  better  than  fats.  In  general,  they  can 
replace  each  other  according  to  the  law  of  isodynamics. 


170  HUMAN  PHYSIOLOGY 

Gelatin  also  shields  proteids,  and  even  more  so  than 
carbohydrates. 

If,  in  the  above  assumed  case  where  nutritive  equilibrium 
is  maintained  with  a  mixed  diet,  the  amount  of  fat,  carbo- 
hydrate, or  gelatin  is  increased  while  the  amount  of  proteid 
remains  constant,  the  proteid  saving  is  slight.  In  such 
cases,  the  gelatin  may  shield  30^  of  the  proteids,  the  carbo- 
hydrates 15$,  and  the  fats  still  less.  But  the  shielding  of 
proteids  is  much  more  effective  when,  simultaneously  with 
an  increase  in  the  other  .foodstuffs,  the  amount  of  proteids  is 
decreased.  When  the  proteid  of  the  food  is  replaced  by  fat, 
carbohydrates,  or  gelatin,  a  much  smaller  quantity  of  proteid 
is  able  to  keep  the  body  proteid  constant  than  if  the  diet 
consists  chiefly  of  proteids.  The  minimum  amount  of  pro- 
teid in  a  mixed  diet,  i.e.  the  absolutely  necessary  proteid 
(see  page  11  7),  is  for  a  man  about  70  g  daily;  but  it  has 
been  observed  that  for  a  short  time  he  can  maintain  his 
body  proteid  with  40  g  of  food  proteids.  But  with  such 
small  quantities  of  proteids  more  fat  and  carbohydrates  must 
be  supplied  than  would  strictly  follow  from  the  law  of 
isodynamics.  The  foodstuffs  which  can  shield  the  proteids 
differ  from  each  other  in  this  capacity;  the  gelatin  shields 
proteids  best,  then  the  carbohydrates,  and,  least  of  all,  the 
fats.  In  regard  to  fats  it  must  be  added  that  the  eating  of 
very  great  quantities  may  increase  the  consumption  of  pro- 
teids. 

If,  in  a  sufficient,  mixed  diet,  the  proteids  are  increased, 
the  following  results: 

1.  The  extra  proteid  is,  as  in  pure  proteid  diet,  in  part 
deposited  in  the  body,  and  part  used  up.  Hence  in  a 
mixed  diet  also,  an  increase  in  the  supply  of  proteid  causes 
an  increase  in  proteid  consumption. 

2.  But  by  this  increase  in  proteid  consumption  the  oxida- 
tion of  fats  and  carbohydrates  is  somewhat  lessened,  so  that 
fat  may  be  deposited. 

V  In  this  case  also,  fats  and  carbohydrates  spare  the 
proteids  to  such  an  extent  that  a   greater  part  of  the  proteid 


METABOLISM  171 

is  deposited   and  a   smaller  part  oxidized   than  occurs   in  an 
exclusive  proteid  diet. 

From  'what  has  thus  far  been  said,  it  follows  that  the 
various  foodstuffs  are  not  of  the  same  value  for  the  organism. 
In  general,  the  body  has  the  tendency  to  be  less  sparing 
with  the  proteids  than  with  the  fats  and  carbohydrates. 

It  also  appears  that  the  body  can  maintain  its  equilibrium 
bv  foodstuffs  mixed  in  various  proportions.  The  question 
is,  which  is  the  most  suitable  mixture  ?  The  most  suitable, 
or  the  rational  diet  for  an  adult  man,  is  100  g  proteid,  60  g 
fat,  400  g  carbohydrates.  These  figures  have  been  obtained 
by  various  experiments  in  metabolism  in  men.  From  the 
experiments  it  has  been  observed  that  the  figures  do  not 
differ  to  any  large  extent  with  the  occupation  and  place  of 
dwelling  of  the  subject  experimented  upon. 

If  the  60  g  of  fat  are  changed,  according  to  the  law  of 
Isodynamics,  into  carbohydrates,  the  proportion  of  proteids 
and  carbohydrates  in  the  daily  meal  is  as  I   :  5.5. 

If,  in  feeding,  the  object  is  not  only  to  keep  the  body 
weight  constant  but  to  increase  either  the  flesh  or  the  fat  in 
the  bod}",  more  foodstuffs  must  be  taken  in.  But  to  increase 
either  the  bod}-  flesh  or  fat,  it  is  not  a  matter  of  indifference 
which  foodstuff  is  increased. 

The  laying  up  of  flesh  can  only  be  produced  by  proteid 
food ;  for  from  fat  and  carbohydrates  no  flesh  can  be 
formed.  But,  by  increasing' the  proteids  of  a  diet  predomi- 
nating in  proteids,  little  flesh  is  laid  up.  For  the  laying  up 
of  flesh  the  most  suitable  diet  is  a  moderate  amount  of 
proteids  besides  large  quantities  of  fats  and  carbohydrates. 
But  if  considerable  flesh  is  to  be  laid  up,  other  conditions 
than  the  nature  of  the  food  play  an  important  part.  For 
example,  the  laying  up  of  flesh  (muscles)  is  especially  favored 
by  proper  muscular  exercise  (training). 

Fattening  of  the  body. — The  fat  laid  up  by  the  body 
originates  from  : 

(a)  The  fat  in  the  food ;  for  if  a  fat  containing  specific 
constituents  (rape-seed  containing  erucic  acid)  normally  not 


f72  Hi  MAN   PHYSIOLOGY 

found    in    the   body  is    added    to   the   food,    we    find   this   fat 
deposited  in  the  body. 

(^)  The  carbohydrates  of  the  food  from  which  by  reduc- 
tion and  synthesis  fat  is  formed.  By  a  diet  rich  in  carbo- 
hydrates glycogen  and  fat  are  deposited  in  the  body. 
Consequently  the  respiratory  quotient  may  be  greater  than 
one;  i.e.  carbohydrates  must  have  been  reduced  and  changed 
to  fats  in  the  bod}'.  By  this  process  oxygen  would  be  set 
free,  which  could  then  be  utilized,  in  connection  with  the 
inhaled  oxygen,  in  the  formation  of  carbon  dioxide. 

(c)  It  has  been  supposed  that  fats  can  be  formed  from 
proteids,  but  no  sufficient  proofs  have  been  furnished. 

For  the  purpose  of  laying  up  fat  the  best  diet  consists  of 
a  moderate  amount  of  proteid  and  an  abundant  supply  of  fat 
and  carbohydrate. 

3.  The  effect  of  water  and  salts. — Increase  of  water  taken 
up  does  not  change  the  amount  of  metabolism,  but  during 
the  first  day  the  excretion  of  nitrogen  is  increased,  due  to 
a  better  washing  away  of  the  nitrogenous  end-products  of 
metabolism. 

Neither  does  increase  in  sodium  chloride  produce  any 
changes  in  the  extent  of  metabolism. 

4.  Effects  of  spices. — Alcohol  does  not  change  the  meta- 
bolism. Alcohol,  like  the  other  non-nitrogenous  foodstuffs, 
is  completely  oxidi/x-d  soon  after  being  taken  into  the  body 
and  can  therefore  replace  fats  and  carbohydrates.  But,  as 
alcohol  is  a  strong  nerve  poison,  it  cannot  be  regarded  as  a 
valuable  material  for  metabolism. 

Concerning  the  effects  of  spices  upon  metabolism,  authors 
differ  widely. 

5.  Effects  of  oxygen. — Voluntary  increase  or  decrease  in 
the  amount  of  respiration  has  no  effect  upon  metabolism,  for 
the  taking  up  of  oxygen  and  the  giving  off  of  carbon  dioxide 
is  not  altered  by  increased  or  decreased  ventilation  during 
a  few  minutes.  The  increased  activity  of  the  muscles  of 
respiration  may,  of  course,  influence  metabolism.  Diminu- 
tion in  the  amount  of  haemoglobin  in  the  blood,  by  loss  of 


METABOLISM  i?3 

half  the  blood,  produces  no  change  in  the  extent  of  meta- 
bolism, for  the  lack  of  oxygen  is  completely  covered  by 
increased  respiration  and  heart  activity,  so  that  oxyhemo- 
globin is  used  to  better  advantage  than  normally.  But  if 
real  lack  of  oxygen  occurs,  e.g.  in  dyspnoea  or  excessive 
muscle  work,  the  metabolism  does  not  decrease,  but,  on  the 
contrary,  there  is  an  increase  in  the  decomposition  of  pro- 
teids.  But  the  combustion  is,  in  this  case,  incomplete; 
hence  considerable  quantities  of  lactic  acid  are  excreted 
with  the  urine  (see  page  42). 

Increase  or  decrease  in  atmospheric  pressure  has,  within 
certain  wide  limits,  no  effect  on  the  amount  of  combustion 
in  the  bod}-. 

II.  The  effect  of  work  and  loss  of  animal  heat  upon 
metabolism. 

(a)  Effect  of  muscular  activity. — By  muscular  work  the 
respiratory  metabolism  and  all  the  processes  of  combustion 
are  increased.  The  combustion  process  may  be  increased 
four  or  five  times  the  normal  amount.  During  moderate 
work  the  respiratory  quotient  is  the  same  as  during  rest. 
But  during  excessive  work  the  increase  in  the  excretion  of 
carbon  dioxide  may  be  greater  than  that  of  the  oxygen 
taken  up,  so  that  the  respiratory  quotient  is  increased. 

The  consumption  of  proteids  is  generally  not  increased  by 
work,  hence  the  increase  in  combustion  must  be  at  the  ex- 
pense of  non-nitrogenous  substances,  fat,  or  carbohydrates. 
Often,  however,  the  excretion  of  nitrogen  is  also  increased 
by  muscular  activity ;  this  is  always  the  case  in  exclusive 
or  predominating  proteid  diet.  But  if  sufficient  fats  or 
carbohydrates  are  present  in  the  mixed  diet,  there  is  no  in- 
crease in  nitrogenous  excretions.  During  muscular  activity, 
the  body  generally  consumes  non-nitrogenous  material. 
But  if  the  work  is  very  excessive,  an  increase  in  the  excretion 
of  nitrogen  may  result  even  with  a  mixed  diet  containing 
much  fat  and  carbohydrate.  This  is  perhaps  due  to  the  fact 
that  excessive  work  injures  the  muscle  tissue.  To  maintain 
the  body  at  its  weight  during  work  it  must  be  supplied  with 


J  74  HUMAN   PHYSIOLOGY 

more  food  than  during  rest.  For  work  the  rational  diet  is. 
proteids  130  g,  fat  100  g,  carbohydrate  500  g.  In  this  diet 
the  proteids  are  also  increased  because  a  man  doing  hard 
work  has  a  better  developed  muscular  system  and  therefore 
a  greater  demand  for  proteids  than  a  resting  or  slightly 
active  persor.  Hence  the  proper  diet  of  a  working  man 
serves  not  only  to  replace  material  consumed  but,  as  the 
power  of  work  is  proportional  to  the  amount  of  muscle,  to 
increase  the  amount  of  flesh. 

(J?)  Effect  of  the  work  of  digestion.  —  In  considering  the 
activity  of  the  body,  the  material  and  energy  used  in  the 
processes  of  digestion  and  absorption  must  not  be  omitted. 
Under  digestive  work  we  include  the  activity  of  the  glands, 
the  movements  of  the  alimentary  canal,  and  the  activity 
which  the  epithelial  cells  of  the  intestine  exhibit  in  taking 
up  material  from  the  intestine  and  transferring  it  to  the  blood 
or  lymph.  Hut  it  is  impos'sible  at  present  to  say  how  much 
of  the  increased  metabolism  observed  after  the  taking  up  of 
food  is  due  to  this  increased  activity  and  how  much  is  due 
to  the  increased  supply  of  material  for  combustion.  It  is 
nevertheless  beyond  doubt  that  the  digestive  work  causes  a 
considerable  increase  in  metabolism,  and  it  has  even  been 
asserted  that  the  difference  between  the  metabolism  of  a 
fasting  and  that  of  a  fed  organism  is  entirely  due  to  this 
increase  in  the  activity  of  the  alimentary  canal.  Hut  it  is 
supposed  that  the  energy  for  this  activity  is  not  supplied  by 
fats  or  carbohydrates  but  by  proteids,  for  during  digestion 
the  nitrogenous  excretion  in  the  urine  is  greatest;  hence 
more  proteids  are  consumed  at  this  time. 

(r)  Effect  of  loss  of  body  heat.— The  human  body  main- 
tains its  own  temperature  independently  of  the  external  tem- 
perature. This  body  temperature  is  maintained  at  its  proper 
height  by  continual  combustion  (see  Chapter  XIII).  The 
body  continuously  loses  heat  which  must  be  replaced  by  the 
combustion  of  new  food  material.  The  amount  of  heat 
given  off  depends  upon  the  external  temperature;  the  lower 
this  is,  the  more  heat  is  lost  by  the  body  and  the  more  oxi- 


METABOLISM  175 

dation  must  take  place  in  order  to  maintain  the  body  tem- 
perature. Hence  the  extent  of  metabolism  increases  with 
lowering  of  the  external  temperature  and  decreases  when 
the  external  temperature  increases.  This  change  in  meta- 
bolism affects  chief!)-  the  combusion  of  fats  and  carbo- 
hydrates. The  increase  in  metabolism  during"  loss  of  heat 
is  caused  by  a  reflex  increase  in  combustion  in  the  muscles 
which  produces  muscle  contraction  (shivering). 

The  power  of  the  human  body  to  adjust  itself  to  great 
variations  in  external  temperature  is  limited.  If  the  external 
temperature  is  very  low,  the  loss  of  heat  ma}'  become  greater 
than  the  heat  production  and  the  bod)"  temperature  falls. 
The  lower  the  body  temperature  falls,  the  more  si  owl}-  the 
vital  processes  take  place  and  the  less  heat  is  produced 
until,  at  last,  the  processes  of  combustion  cease  altogether 
and  the  organism  freezes  to  death.  If  the  external  tempera- 
ture is  so  high  that  the  body  produces  more  heat  than  it  can 
give  off,  the  body  temperature  rises.  This  causes  an  in- 
crease in  the  vital  processes  and  more  heat  is  produced  until, 
at  last,  the  body  is  overheated  and  death  results.  In  the 
increased  metabolism  the  consumption  of  proteids  is  also 
increased. 

Within   the   limits   in   which   the   bod)"  can   accommodate 

itself,  a  fall  in  external  temperature  increases  metabolism, 

and  a  rise   decreases   it.      But,    outside   of  these   limits,  the 

effects   are   exactly  the   reverse,  for  a   decrease   in    external 

temperature  causes  a  fall,  and  an  increase,  a  rise  in  the  bod}' 

temperature.      Hence,    in  the   last-mentioned    case,    man   is 

like  the  cold-blooded  animals,  in  which  the  metabolism  rises 

and  falls  with  the  external  temperature. 

But  it  will  be  shown  that,  for  the  regulation  of  the  body  tem- 
perature, besides  the  mechanism  for  regulating  the  metabolism, 
another  and  far  better  mechanism  regulating  the  loss  of  heat  is 
present  (see  page  181). 

{d)  Effect  of  sensory  stimulation  and  psychical  activity. 

— Stimulation  of  the  skin  and  strong  stimulation  of  the 
retina  by  light  increase  the  consumption  of  oxygen  and 
production    of   carbon    dioxide.      Hence    during    sleep    the 


176  HUMAN  PHYSIOLOGY 

respirator)"  exchange  of  gases  is  considerably  decreased. 
Besides,  during  sleep  the  muscular  movements,  except  those 
of  the  heart  and  respirator}'  muscles,  are  reduced  to  a  mini- 
mum, and  the  muscle  tonus  also,  which  maintains  the  position 
of  the  body,  is  inhibited.  The  proteid  metabolism  is  not 
affected  by  sleep. 

It  has  not  yet  been  definitely  proven  that  psychical  activity 
has  any  effect  upon  metabolism. 

III.  Effect  of  the  size  of  the  body,  age,  and  sex  upon 
metabolism. — Small  persons  have  a  relatively  greater  meta- 
bolism than  large  persons,  for,  since  in  them  the  surface  by 
which  heat  is  lost  is  larger  in  proportion  to  the  heat-produc- 
ing mass  than  in  large  individuals,  the  smaller  person  must 
produce  relatively  more  heat  in  order  to  keep  a  constant 
body  temperature  than  the  larger  person.  Hence  the 
metabolism  of  a  child  is  relatively  greater,  although  abso- 
lutely smaller  than  that  of  the  adult  (see  page  118).  In  old 
age  the  metabolism  is  smaller  than  in  the  prime  of  life. 
Because  of  differences  in  the  size  of  body,  the  metabolism  in 
a  woman  is  less  than  in  a  man,  therefore  the  diet  for  woman 
is  also  less.  An  adult,  resting  woman  needs  90  g  proteids, 
40  g  fat,  and  350  g  carbohydrate  daily.  During  pregnancy 
the  metabolism  is  increased.  Sex  itself  has  no  influence 
upon  metabolism. 


PART    II 

THE  TRANSFORMATION   AND   SETTING 
FREE   OF   ENERGY 

The  potential  chemical  energy  of  the  body  substance  is 
changed  to  kinetic  energy  (heat  and  muscular  activity  by 
the  physiological  combustion. 

The  cause  of  the  transformation  of  energy  lies  partly  in 
the  living  substance  itself,  partly  in  the  stimulations  "which 
act  upon  the  living  substance.  The  stimulations  either  have 
their  origin  in  the  body  itself  and  serve  to  regulate  the  rela- 
tion existing  between  the  individual  organs,  or  they  originate 
in  the  external  world  and  serve  by  their  stimulating  effect 
to  connect  the  body  with  its  environment.  To  receive  these 
external  stimulations,  the  body  is  provided  with  special 
organs,  the  sense  organs.  The  stimulation  is  carried  from 
the  sense  organs  by  means  of  a  special  apparatus,  the 
nervous  system,  to  the  muscles  in  which  the  transformation 
of  energy  chiefly  takes  place. 

The  study  of  the  transformation  and  setting  free  of  energy 
may  be  divided  into  the  following  chapters : 

i .    Animal  heat. 

2.  Muscular  contraction. 

3.  Functions  of  the  nervous  system. 

4.  Functions  of  the  sense  organs. 

177 


CHAPTER    XIII 

ANIMAL   HEAT 

i.  Heat  production. — In  the  animal  body  the  heat  formed 
originates  from  the  potential  chemical  energy  of  the  food. 
In  a  resting  body,  in  which  no  energy  is  used  up  for  ex- 
ternal work,  as  much  heat  is  formed  as  corresponds  to  the 
potential  chemical  energy  set  free  during  combustion. 
Hence  the  law  of  conservation  of  energy  holds  good  also  for 
the  transformation  of  energy  in  the  living  body. 

Heat  can  also  be  imparted  to  the  body  by  the  taking  up  of  food 
and  drink  wanner  than  the  body,  but  this  is  of  little  importance 
and  does  not  occur  regularly. 

In  the  working  body  the  energy  transformed  is  equal  to 
the  heat  produced  and  the  external  work  done. 

The  work  of  the  heart,  of  the  muscles  of  the  alimentary  canal, 
and  of  the  respiratory  apparatus  is  not  reckoned  with  the  external 
work,  for  their  work  is  transformed  into  heat  in  the  body. 

The  unit  of  heat  is  the  caloric.  A  calorie  is  the  amount  of  heat 
needed  to  raise  i  kg  of  water  from  o°  to  i°  C. 

The  unit  of  work  is  the  kilogrammeter,  which  is  the  work 
done  by  raising  i  kg  the  distance  of  I  meter.  One  calorie 
equals  425  kilogrammeters. 

The  chemical  energy  of  an  oxidizable  substance  is  indi- 
cated by  its  heat  of  combustion,  i.e.  the  heat  set  free  by  the 
complete  oxidation  of  the  substance.  The  following  table 
gives  the  heat  of  combustion  of  a  few  substances : 

Hydrogen 34.0  calories. 

Carbon 8.0 

Fat 9-3 

Sugar 3-7 

Starch 4-5 

Proteid 5.5 

178 


ANIMAL  HEAT  179 

Proteids  are  not  completely  oxidized  in  the  body,  for  the 
urea  formed  from  it  can  still  undergo  oxidation.  If  the  heat 
value  of  urea  is  subtracted  from  that  of  proteid,  there  remain 
for  one  gram  of  proteid  4. 1  calories. 

The  physiological  heat  values  are : 

For  I  g  proteid  4.1  cal.  ;  I  g  fat  9.3  cal.  ;  1  g  carbo- 
hydrate 4. 1  cal. 

As  far  as  their  heat  production  for  the  organism  is  con- 
cerned, the  following  substances  are  isodynamic :  2.3  g 
proteid  (or  gelatin)  =  I  g  fat  =  2.3  carbohydrate. 

If  the  extent  of  metabolism  is  known,  we  can  calculate 
from  the  heat  value  of  the  substances  oxidized  the  amount 
of  heat  formed.  Conversely,  by  finding  the  amount  of  heat 
produced  we  can  calculate  the  extent  of  metabolism ;  but 
this  calculation  is  not  conclusive  as  to  the  individual  kinds 
of  foodstuffs  used. 

The  production  of  heat  is  measured  by  the  water-  or  air-calo- 
rimeter. In  the  -water- calorimeter  the  body  is  placed  in  a  tin 
case  which  is  surrounded  by  a  layer  of  water.  The  heat  given  off 
by  the  animal  heats  this  water.  The  respiratory  air  is  supplied 
through  tubes  of  which  the  one  carrying  the  exhaled  air  passes 
through  the  layer  of  water  which  surrounds  the  case,  so  that  the 
heat  of  the  exhaled  air  is  imparted  to  the  water  also.  From  the 
increase  in  temperature  of  the  water,  the  amount  of  heat  lost  by 
the  body  can  be  calculated.  This  amount  equals  the  heat  formed, 
for  the  body  temperature  is  the  same  at  the  end  as  at  the  beginning 
of  the  experiment.  In  the  air-calorimeter  the  tin  case  is  sur- 
rounded by  a  layer  of  air  whose  expansion  by  the  heat  measures 
the  amount  of  heat  set  free. 

The  adult  resting  human  being  produces  in  twenty-four 
hours  about  2400  calories,  or  in  one  hour  100  calories, 
This  is  34  calories  per  kilogram  of  body  weight  in  twenty- 
four  hours,  and  1.4  cal.  in  one  hour. 

The  amount  of  heat  produced  is  dependent  upon  the  same 
circumstances  as  metabolism.  Muscle  activity  increases 
heat  production,  for,  of  the  extra  energy  set  free  thereby, 
only  a  part  can  be  used  in  the  performance  of  work,  the  rest 
being  changed  to  heat.  Of  all  the  energy  set  free  by  a 
working  body,  at  most  only  one-fourth  can   be  utilized   for 


l8o  HUMAN   PHYSIOLOGY 

mechanical  work;  the  remaining  three-fourths  is  set  free  as 
heat.  During  hard  work  an  adult  man  produces  in  twenty- 
four  hours,  for  ever}'  kilogram  of  body  weight,  an  amount 
of  heat,  including  the  external  work,  equal  to  55  calorics. 

2.  The  loss  of  heat. — The  body  continuously  loses  heat: 

(1)  By  radiation  and  conduction  from  the  surface  of  the 
body  to  the  surrounding  air,  which,  as  a  rule,  is  colder  than 
the  body. 

(2)  By  the  evaporation  of  water  from  the  skin,  especially 
by  the  secretion  of  sweat.  By  this  means  the  body  can  lose 
heat  when  the  surrounding  medium  has  a  higher  temperature 
than  the  body  itself. 

(3)  By  exhaling  air  which  has  been  heated  to  the  body 
temperature  and  is  saturated  with  water  vapor.  The  water 
vapor  is  imparted  to  the  expired  air  by  the  evaporation  of 
water  from  the  mucous  membranes  of  the  air  passages. 

(4)  By  heating  up  the  ingested  food  and  drink  ;  in  other 
words,  by  voiding  excretions  heated  to  the  body  tempera- 
ture (urine,  faeces). 

Of  all  the  heat  lost  by  the  bod}-,  about  80$  is  lost  by 
radiation,  conduction,  and  evaporation  from  the  skin;  about 
15'  by  evaporation  from  the  mucous  lining  of  the  air 
passages ;  one  half  of  the  rest  by  expired  air,  and  the  other 
half  by  the  excretions. 

The  amount  of  heat  which  is  lost  in  each  of  these  ways  is 
variable.  The  lower  the  external  temperature,  the  more 
heat  is  lost  by  conduction  from  the  skin  and  by  heating  the 
inhaled  air;  the  loss  of  heat  by  evaporation  is  greater,  the 
drier  the  air  and  the  greater  the  amount  of  sweat  secreted. 
The  heat  lost  by  expired  air  depends  upon  the  frequency 
and  depth  of  respiration. 

3.  Body  temperature.  —  Man  belongs  to  the  warm- 
blooded or  homoiothermic  animals  whose  bod}-  temperature 
is,  apart  from  very  slight  variations,  constant.  The  body 
temperature  of  man  is  36.5—  37. 50  C. 

The  body  temperature  is  measured  by  placing  a  thermometer  in 
the  rectum,  vagina,  mouth,  or  axilla,  the  arm  being  placed  in  the 
proper  position  around  the  thermometer. 


ANIMAL   HEAT  t8i 

The  blood  streams  from  the  tissues  where  most  of  the 
heat  is  produced  (muscles  and  large  glands)  to  the  skin, 
where  it  becomes  cooled.  The  temperature  of  the  muscles 
is  therefore  somewhat  higher,  and  that  of  the  skin  lower, 
than  that  of  the  blood. 

The  body  temperature  shows  some  regular  minor  varia- 
tions;  shortly  after  midnight  it  is  lowest  (36.  5  °),  while  in  the 
afternoon  it  is  highest  (37-5°).  It  is  somewhat  increased  by 
the  partaking  of  food  and  by  muscle  activity. 

Mammals  have  about  the  same  body  temperature  as  man;  in 
birds  it  is  higher  (40-450).  The  body  temperature  of  cold-blooded 
or  poikilothermic  animals  is  a  few  degrees  (i-4°)  higher  than  that 
of  the  surrounding  medium  (provided  they  have  not  been  placed 
in  a  warmer  or  colder  medium  just  previous  to  the  measurement). 

Hibernating  mammals  are,  during  their  winter  sleep,  like  cold- 
blooded animals. 

4.  Regulation  of  body  temperature. — The  body  tempera- 
ture remains  constant  wrhen  the  production  of  heat  equals  the 
loss  of  heat.  If  changes  occur  in  the  production  of  heat 
(e.g.  by  muscular  activity)  or  in  the  loss  of  heat  (e.g.  in  hot 
or  cold  weather),  the  production  and  loss  of  heat  must  again 
be  regulated  in  order  to  keep  the  body  temperature  con- 
stant. Concerning  the  nature  of  the  regulation  of  tempera- 
ture by  the  nervous  system  little  is  known. 

Some  authors  think  that  there  are  in  the  central  nervous  system 
certain  centres  (heat  centres)  by  which  the  mechanism  for  regula- 
tion of  body  temperature  is  governed.  But  the  account  given  of 
these  centres  and  their  mode  of  action  is  not  satisfactory. 

By  the  regulation  of  temperature  both  the  production  and 
the  loss  of  heat  can  be  varied. 

Changes  in  the  production  of  heat  occur  when  the  loss  of 
body  heat  is  altered  by  variations  in  the  temperature  of  the 
surrounding  medium.  In  cold  weather  the  production  of 
heat  is  increased  to  such  an  extent  that  involuntary  muscular 
contraction  takes  place  (chattering  of  teeth,  shivering). 

In  small  animals  the  proportion  of  the  surface  by  which 
heat  can  be  lost  to  the  heat-producing  body  mass  is  greater 
than   in  larger  animals.      Therefore,  in  order  to   maintain  a 


1 82  HUMAN  PHYSIOLOGY    ' 

constant  body  temperature  smaller  animals  must  produce 
more  heat  per  kilogram  of  body  weight  than  larger  animals. 
The  adult  human  being  produces,  at  rest,  per  kilo-hour  1.4 
calories,  while  a  child  four  years  old  produces  about  2.5 
calories,  a  rabbit  5.6  calories. 

If  the  loss  of  heat  is  stated  in  terms  of  the  unit  of  body  surface, 
it  is  found  that  it  is  about  the  same  in  animals  of  various  sizes. 
The  amount  of  heat  lost  by  man  per  square  meter  is  about  1 200 
calories  in  24  hours. 

Variations  in  the  loss  of  heat  take  place  because  of: 

(1)  Increased  or  decreased  supply  of  blood  to  the  skin, 
whereby  the  heat  carried  to  the  cooling  body  surface  is  in- 
creased or  decreased.  The  supply  of  blood  to  the  skin  is 
increased  by  the  dilation  of  the  cutaneous  vessels  and  the 
increase  of  pulse  rate;  it  is  decreased  by  the  contraction  of 
the  vessels  and  the  decrease  of  the  pulse  rate. 

(2)  Secretion  of  sweat,  which,  by  evaporation,  cools  the 
body. 

(3)  Increase  or  decrease  in  the  frequency  or  depth  of  the 
respirations,  whereby  more  or  less  heat  is  given  off  by  the 
expired  air. 

Muscular  activity,  by  which  more  heat  is  produced,  or 
raising  of  the  external  temperature  (warm  weather)  are  fol- 
lowed by  perspiration,  increased  pulse  and  respiration,  and 
dilation  of  the  cutaneous  vessels ;  lowering  of  the  external 
temperature  (cold  weather)  causes  constriction  of  the  cuta- 
neous vessels. 

We  can  voluntarily  regulate  the  loss  of  heat  by  warming 
ourselves,  by  clothing,  by  the  position  of  the  body,  and  by 
partaking  of  cold  or  warm  drinks.  We  can  regulate  the 
production  of  heat  by  voluntary  muscular  activity.  In 
animals  hairs  and  feathers  serve  to  regulate  the  loss  of  heat. 

Our   ability  to    keep   the  body  temperature    constant    by 
means  of  the  heat-regulating  mechanism  is,  however,  limited. 
This  regulation  of  temperature  fails  when  the  temperature  of 
the    surrounding  medium    is    too   high    or  too   low,    so   that 
changes  in  the  production  or  loss  of  heat  are  no  longer  able 


ANIMAL   HEAT  183 

to  prevent  the  body  temperature  from  rising  or  falling. 
Very  strong  cooling  also  disturbs  the  regulation  of  tempera- 
ture by  paralyzing  the  muscles  of  the  blood  vessels  so  that 
the  cutaneous  vessels  become  dilated  to  an  abnormal  extent. 
When  the  temperature  regulation  fails,  the  body  temperature 
speedily  sinks  below  190  or  rises  about  420  and  death  results. 
In  fever,  the  regulation  of  temperature  is  disturbed ;  the 
production  of  heat  is  increased,  hence  the  body  temperature 
is  abnormally  high. 

Within  certain  limits,  the  heat  production  in  cold-blooded 
animals  is  the  larger,  the  higher  the  temperature  of  the  external 
medium,  for,  in  these  animals,  the  intensity  of  the  combustion 
taking  place  in  the  body  increases  with  the  raising  of  the  external 
temperature. 


CHAPTER    XIV 

GENERAL   MUSCLE    PHYSIOLOGY 

THE  active  movements  of  the  body  are  produced  by  the 
contraction  of  the  muscles  whose  fibres  shorten  in  their 
longitudinal  direction  (contraction).  They  perform  work 
by  the  movement  of  the  parts  connected  with  them  (bones). 

The  physiology  of  the  movement  may  be  divided  into: 

(i)  General  muscle  physiology,  the  study  of  general  properties 
of  muscles. 

(2;  Special  muscle  physiology,  which  treats  of  the  actions  of 
individual  muscles. 

Anatomical  considerations. — The  striated  muscle  is  composed 
of  muscle  fibres,  varying  in  length  up  to  12  cm  and  having  a 
diameter  of  0.01-0.06  mm.  These  fibres  arc  surrounded  and  held 
together  by  connective  tissue  (perimysium  internum  and  ex- 
ternum). In  this  connective  tissue  are  found  nerves  and  blood 
vessels.  The  muscle  fibre  is  composed  of  a  bundle  of  parallel 
fibrils,  between  which  there  is  a  protoplasmic  substance,  the 
sarcoplasm.  The  fibre  is  surrounded  by  a  structureless  covering, 
the  sarcolemma.  Directly  beneath  the  sarcolemma  lie  the  muscle 
corpuscles,  spindle-shaped  and  nucleated  protoplasmic  bodies. 

The  smooth  muscle  is  composed  of  fibre-like  cells  without  any 
sheath.  The  cells  vary  in  length  and  diameter  up  to  0.5  mm  and 
0.02  mm  respectively  and  contain  rod-like  nuclei.  Sometimes 
fibrils  and  sarcoplasma  are  found  in  smooth  muscles. 

The  fibrils  which  seem  to  contain  the  contractile  part  are,  in 
the  smooth  muscle,  composed  throughout  their  entire  length  of 
doubly  refracting  parts  (anisotropic),  while  the  striated  muscle 
fibril  is  composed  of  alternate  doubly  and  singly  refracting 
(isotropic)  parts.  The  striated  appearance  of  muscles  is  caused 
by  the  alternate  arrangement  of  parts  which  vary  in  transparency. 

In  the  middle  of  each  isotropic  (light)  disk  there  is,  in  the 
striated  muscle,  a  narrow  dark  band  called  the  intermediate  disk, 
or  membrane  of  Krause,  on  both  sides  of  which  there  is  another 
dark  band  called  the  secondary  disk.      In  the  centre  of  the  aniso- 

184 


GENERAL   MUSCLE   PHYSIOLOGY  185 

tropic  (dark)  disk  there  is  a  narrow  light  band,  called  the  median 
disk  of  Hens  en.  The  physiological  importance  of  these  structures 
is  still  unknown. 

By  double  refraction  exhibited  by  many  crystals  a  single  ray  of 
light  is  broken  up  into  two  rays.  The  double  refractive  muscle 
substance  has  an  optical  axis  in  the  longitudinal  direction  of  the 
fibres,  in  which  the  light  is  broken  but  once.  The  importance  of 
this  doubly  refracting  substance  of  the  muscle  fibrils  for  the 
property  of  contractility  is  not  known. 

The  motor-nerve  fibres  are  connected  with  the  muscle  fibres, 
the  axis  cylinder  of  the  nerve  fibre  forming  a  flat  arborization 
(end-plate)  which  lies  in  contact  with  the  muscle  fibres. 

Nearly  all  the  striated  muscles  can  be  voluntarily  stimulated, 
eicept  the  heart  muscle.  The  stimulation  of  most  of  the  smooth 
muscles  is  not  subject  to  our  will,  except  the  muscle  of  accommo- 
dation of  the  eye. 

The  contraction  of  the  muscle  takes  place  when  it  is 
stimulated.  In  a  stimulated  muscle  the  physiological  com- 
bustion is  increased,  whereby  energy  is  set  free  which  pro- 
duces the  contraction  and  performs  the  work.  The  manner 
in  which  the  potential  chemical  energy  is  transformed  into 
mechanical  work  is  still  unknown. 


1.   THE    RESTING    MUSCLE 

1 .   Chemical  properties  of  a  resting  muscle. 

[a)  Composition  of  muscles. — The  reaction  of  a  resting 
muscle  is  neutral  or  feebly  alkaline.  A  muscle  contains 
25$  solids,  which  include: 

1.    Proteids  2O<f0. 

If  a  fresh  frozen  muscle  is  cut  up  and  the  extract  filtered  at 
about  30,  a  cloudy  neutral  or  feebly  alkaline  fluid  is  obtained. 
This  is  the  fluid  contents  of  the  fibres  or  the  muscle  plasma.  At 
higher  temperatures  it  coagulates  spontaneously  and,  the  higher 
the  temperature,  the  more  speedily  it  clots.  The  coagulation  is 
due  to  the  formation  of  an  insoluble  proteid,  myosin,  from  a 
soluble  proteid  of  the  muscle  plasma,  myosinogen,  by  the  action 
of  the  ferment.  Coagulation  also  occurs  during  rigor  mortis. 
The  myosin  forms  about  20$  of  the  muscle  proteids. 

The  solution  which  is  left  after  myosin  has  been  formed  is  called 
the  muscle  serum.      It  has  an  acid  reaction  and  contains  about 


1 86  HUMAN  PHYSIOLOGY 

80/0  muscle  albumin.  The  remainder  is  chiefly  composed  of  a 
proteid,  called  myogen. 

The  muscle  also  contains  an  undissolved  proteid  of  unknown 
nature,  collagen,  and  the  nuclein-like  phosphocarnic  acid  which, 
by  splitting  up,  yields  phosphoric  acid,  a  sugar-like  product,  lactic 
acid,  and  carnic  acid,  a  substance  belonging  to  the  peptones. 

In  addition  to  the  above-named  proteids,  the  muscles  contain 
a  pigment,  myohaematin,  which  is  identical  with  the  haemoglobin 
of  the  blood;  but  it  is  not  derived  from  haemoglobin,  for  animals 
without  blood  also  have  this  pigment  in  their  muscles. 

2.  Carbohydrates,  chiefly  glycogen,  stored  up  between 
the  muscle  fibrils  ;  grape-sugar  in  small  and  varying  amounts  ; 
inosit. 

3.  Fats,  chiefly  deposited  in  the  intramuscular  connective 
tissue.      The  amount  varies  with  nutrition. 

4.  End-products  of  metabolism,  chiefly  keratin  and 
xanthin  bases;   also  sarcolactic  acid. 

5.  Salts,  especially  potassium  phosphate. 

Muscles  contain  carbon  dioxide,  but  no  free  oxygen  can 
be  obtained  from  them. 

(7;)  Chemical  processes  in  the  resting-  muscle.  —  The 
physiological  combustion  in  the  resting  muscle  manifests 
itself  by  the  consumption  of  oxygen  and  the  production  of 
carbon  dioxide.  This  is  evident  from  the  fact  that  arterial 
blood  is  changed  to  venous  blood  in  the  muscles. 

2.  Mechanical  properties  of  a  resting  muscle. — The 
muscle  is  elastic  and,  in  the  longitudinal  direction  of  its 
fibres,  extensible.  During  this  extension,  the  length  of  the 
muscle  increases,  its  thickness  decreases ;  its  volume  under- 
goes no  change. 

The  elongation  during  extension  is  not  proportional  to  the 
weight  which  causes  the  extension,  for  the  extension  pro- 
duced by  one  and  the  same  weight  is  the  less,  the  more  the 
muscle  is  already  stretched.  Hence  the  curve  of  extension, 
i.e.  the  curve  whose  abscissa  represents  the  weight  and 
whose  ordinate  represents  the  length  of  the  muscle,  is  not  a 
straight  line,  but  a  hyperbola  (see  page  192). 


GENERAL   MUSCLE  PHYSIOLOGY  187 


2.   THE    STIMULATED    OR    ACTIVE    MUSCLE 

1.   Chemical   processes   in   the   active  muscle. — In  the 

active  muscle  the  processes  of  combustion  are  enormously 
increased.  During  muscular  activity  the  consumption  of 
oxygen  and  the  formation  of  carbon  dioxide  maybe  increased 
to  four  or  five  times  that  during  rest.  During  this  activity 
more  carbohydrates  or  fats  are  used,  while  the  consumption 
of  proteid  remains  the  same,  if  sufficient  fat  and  carbohy- 
drate are  present.  But  if  these  are  not  present  in  sufficient 
quantities,  the  muscular  activity  takes  place  at  the  expense 
of  proteid.  This  is  evident  from  the  metabolism  of  the  body 
during  rest  and  work.  The  taking  up  of  oxygen  and  the 
giving  off  of  carbon  dioxide  are  always  enormously  increased 
by  muscular  activity,  but  the  nitrogenous  excretions  are  only 
increased  when  the  food  does  not  contain  sufficient  non- 
nitrogenous  substances  to  supply  the  energy  for  the  work, 
■e.g.  during  purely  proteid  diet. 

The  respiratory  quotient  is  not  changed  by  muscular 
activity,  if  the  work  is  not  extreme ;  but  if  the  work  is 
fatiguing,  it  is  increased. 

The  amount  of  glycogen  in  the  muscles  and  in  the  liver 
is  decreased  by  work.      Body  fat  may  also  be  lost  by  work. 

The  active  muscle  has  an  acid  reaction.  Sarcolactic  acid 
of  the  muscle  is  increased  by  activity. 

Although  no  trace  of  free  oxygen  is  present  in  the  muscles  of  a 
irog,  still  an  excised  frog-muscle  placed  in  an  atmosphere  free  of 
oxygen  can  do  work.  They  therefore  contain  oxygen  stored  up 
in  the  form  of  chemical  compounds  which  can  be  used  when 
necessary. 

Muscles  of  warm-blooded  animals  contain,  at  best,  only  a  small 
supply  of  stored-up  oxygen,  for  they  lose  their  irritability  soon 
after  the  supply  of  arterial  blood  is  cut  off. 

The  amount  of  substances  capable  of  extraction  with  water  is 
decreased  by  activity,  while  those  extracted  by  alcohol  are 
Increased.  It  is  said  that  the  amount  of  phosphocarnic  acid 
£phosphorfleischsaure]  in  the  muscles  is  decreased  by  activity. 


l88  HUMAN  PHYSIOLOGY 

2.   The  external  phenomena  during  the  transformation 
of    energy  in    an  active   muscle. — The    transformation    of 
energy  reveals    i-tself  in   definite   mechanical,    thermal,    and 
electrical  changes  in  the  muscles. 
A.  Mechanical  changes  in  the  stimulated  muscle. 

(a)  Contraction. — The  stimulated  muscle  shortens  in  its 
longitudinal  direction,  the  diameter  increases,  while  the 
volume  remains  the  same. 

Both  the  anisotropic  and  the  isotropic  bands  of  the  striated 
muscle  change  in  the  same  sense  as  the  whole  muscle. 
That  the  volume  of  the  anisotropic  part  is  increased,  while 
that  of  the  isotropic  part  is  slightly  decreased,  is  explained  by 
the  passing  of  water  from  the  isotropic  to  the  anistropic  part. 
Besides  this,  the  optical  difference  between  the  two  parts 
becomes  less. 

Twitching. — If  a  muscle  is  acted  upon  by  a  stimulus  last- 
ing for  but  a  short  time  (by  an  induced  electric  current),  it 
draws  itself  together  rapidly  and  then  again  immediately 
lengthens.      This  is  called  a  twitch. 

The  length  of  time  consumed  by  a  twitch  is  investigated  by  the 
graphic  method.  The  muscle  is  connected  with  a  writing-lever 
which  is  moved  by  its  contraction  and  writes  its  movement  on  a 
travelling  surface.  Such  an  apparatus  for  the  graphical  registra- 
tion of  a  muscle  contraction  is  called  a  myograph. 

An  isotonic  contraction  is  a  contraction  during  which  the  tension 
(tonus)  of  the  muscle  remains  constant.  The  isotonic  contraction 
curve  shows  the  duration  of  the  contraction  during  constant  ten- 
sion. To  obtain  such  a  curve  a  writing-lever  must  be  used  which 
is  thrown  upward  as  little  as  possible  by  the  contracting  muscle. 
A  light  lever  is  used  and  a  weight  is  hung  as  near  the  axis  as 
possible,  while  the  muscle  is  attached  to  the  lever  at  considerable 
distance  from  the  axis.  During  normal  physiological  conditions, 
a  muscle  does  not  contract  isotonically.  but  always  with  change  in 
tension. 

An  isometric  contraction  is  a  contraction  in  which  the  shortening 
of  the  muscle  is  completely  prevented,  so  that  tension  is  produced 
without  the  shortening  of  the  muscle.  The  changes  in  tension  in 
an  isometric  contraction  can  be  registered  by  the  so-called  tension 
recorder. 

A  noticeable  length  of  time  elapses  between  the  moment 
of  stimulation  and  the  beginning  of  contraction  ;   this  time  is 


GENERAL   MUSCLE   PHYSIOLOGY 


189 


called  the  latent  period.  The  contraction  occurs  at  first 
with  increasing  and  then  with  decreasing  rapidity  till  the 
maximum  is  reached ;  after  this  the  muscle  relaxes,  at  first 
rapidly,  but  soon  more  slowly  until  it  has  acquired  its  former 
length.  Frequently  the  relaxation  is  not  complete,  especially 
when  the  load  of  the  muscle  is  small  (see  Fig.  9). 

The  length  of  the  latent  period  for  the  skeletal  frog- 
muscle  is,  at  room  temperature,  about  0.0 1  second,  for 
human  muscle  0.004  to  0.0 1  second,  for  smooth  muscle  0.4 
to  0.8  second. 


Z 

Fig.  9 — Isotonic  Contraction  of  a  Frog-muscle. 
J,  curve  of  contraction ;  r,  moment  of  stimulation;  from  r  to  a,  latent  period; 
from  a  to  /'.    period    of  increasing    energy;    from    b  to   c.  period   of  decreasing 
energy;    Z,     time-curve    produced   by    a    vibrating    tuning  fork    (each   vibration 
equals  o.oi  second). 

The  duration  of  contraction  for  a  skeletal  muscle  of  a  frog 
at  room  temperature  is  about  o.  1  to  o.  1 5  second,  for  a  human 
muscle  a  little  less,  for  a  smooth  muscle  1  to  3  minutes. 
Various  striated  muscles  of  the  same  animal  contract  with 
different  rapidity,  e.g.  the  gastrocnemius  of  a  frog  contracts 
more  rapidly  than  the  hyoglossus.  Many  animals  (rabbits, 
birds)  have  slowly  contracting  striated  muscles  which  have 
a  red  color  and  are  poor  in  sarcoplasm,  while  they  also  have 
rapidly  contracting  muscles  which  are  white  and  contain 
much  sarcoplasm. 

The  extent  of  the  contraction  (height  of  contraction;  in  a 
maximal  contraction  of  a  frog-muscle  is  about  one-fifth  of 
the  length  of  the  fibre. 

Conditions  influencing  the  contraction. 

1.  Temperature.  —  Between  the  temperature  of  —  400  and 
-f-  40°  C.    the    duration   of   the  contraction    and    the    latent 


190  HUMAN   PHYSIOLOGY 

period  are  the  shorter  the  higher  the  temperature.  The 
height  of  the  contraction  also  changes  with  the  temperature, 
but  it  is  not  increased  merely  with  the  raising  of  temperature, 
for  a  cold  muscle  may  give  greater  contraction  than  a  warm 
muscle. 

2.  Tlic  load. — In  general,  the  height  of  the  contraction  is 
less  the  greater  the  load  of  the  muscle.  But  it  must  be 
observed  that  the  height  of  contraction  of  a  muscle  without 
an}'  load  is  slightly  less  than  that  of  a  moderately  loaded 
muscle. 

3.  Fatigue. — If  a  muscle  has  made  many  successive  con- 
tractions, the  duration  of  the  contraction  and  latent  time 
increases;  the  height  of  the  contractions  at  first  slightly 
increases,  but  later  on  gradually  decreases. 

Concerning  the  influence  of  the  strength  of  the  stimulus 
upon  contraction  see  page  197. 

Wave  of  contraction. — Though  but  a  limited  portion  of 
a  muscle  is  stimulated,  the  whole  muscle  contracts.  The 
contraction  is  propagated  in  the  form  of  a  wave  in  both 
directions  from  the  spot  stimulated  throughout  the  muscle 
fibres.  If  the  motor  nerve  of  a  muscle  is  stimulated,  the 
wave  of  contraction  spreads  from  the  place  of  entrance  of  the 
nerve  through  the  fibres. 

The  rapidity  of  the  contraction  wave  is  measured  by 
stimulating  a  certain  part  of  the  muscle  and  placing  two 
recording  lexers  at  unequal  distances  from  the  stimulated 
spot.  The  increase  in  diameter  of  the  muscle  due  to  con- 
traction will  not  meet  the  two  levers  at  the  same  time,  and 
this  difference  in  time  will  represent  the  length  of  time  taken 
by  the  contraction  wave  to  travel  through  the  distance  which 
separates  the  two  lexers. 

The  rate  of  the  contraction  wave  in  the  skeletal  muscle  of 
a  frog  at  room  temperature  is  three  metres  per  second,  for 
the  muscles  of  a  rabbit  four  to  five  metres,  and  for  a  human 
muscle  ten  to  fifteen  metres.  In  smooth  muscles  it  is  ten 
to  fifteen  mm  per  second.  The  rate  is  decreased  by  cooling 
the  muscle  and  by  fatigue.      The  duration  of  the  contraction 


GENERAL   MUSCLE  PHYSIOLOGY  191 

wave  in  the  cross-section  of  a  fibre  is  of  course  less  than  the 
duration  of  contraction  of  the  whole  muscle;  it  is  about  0.05 
to  0.09  second  in  the  frog-muscle.  The  length  of  the  con- 
traction wave  in  the  frog-muscle  is  200— 380  mm. 

In  striated  muscles,  except  in  the  cardiac  muscle,  the 
contraction  does  not  pass  from  one  fibre  to  another  as  it  does 
in  the  smooth  muscles. 

Superposition  of  twitches.  Tetanus. — If  a  muscle  is 
stimulated  by  many  single  stimuli  which  follow  each  other 
so  fast  that  the  interval  between  two  successive  stimulations 
is  less  than  the  duration  of  the  contraction,  the  individual 
twitches  called  forth  by  the  individual  stimulations  combine. 
But  the  increase  in  contraction  which  each  successive 
stimulation  produces  is  smaller  than  that  of  the  preceding. 
Finally  a  maximum  contraction  is  reached  which  cannot  be 
surpassed  by  the  succeeding  stimulations.  If  the  interval 
between  the  stimulations  is  small  enough,  a  lasting  contrac- 
tion is  produced  by  the  combination  of  the  twitches,  which 
is  called  tetanus.  In  a  frog-muscle  tetanus  is  produced  at 
room  temperature  when  about  20  stimulations  per  second  are 
sent  into  the  muscle. 

In  a  muscle  without  any  load,  the  height  of  a  tetanic  con- 
traction may  be  80^  of  the  length  of  the  fibre.  In  a  loaded 
muscle  it  is  less  in  proportion  as  the  load  is  greater. 

It  is  difficult  to  tetanize  the  cardiac  muscle  (see  page  64). 

The  voluntary  muscle  contraction  is  also  tetanic.  This 
is  apparent  from  the  variations  frequently  seen  in  the  con- 
traction of  a  voluntarily  contracted  muscle  which  can  be 
graphically  registered  by  recording  the  thickening  of  the 
muscle.     There  are  about  8  to  12  oscillations  in  one  second. 

Muscle-sound. — If  an  artificially  stimulated  muscle  is  connected 
with  the  ear  by  means  of  a  sound-conductor,  a  sound  is  heard 
which  corresponds  to  the  number  of  oscillations.  From  volun- 
tarily contracted  muscles  a  sound  is  also  heard  (19  vibrations  per 
second),  but  it  is  doubtful  whether  this  sound  is  produced  by  the 
oscillatory  stimulation  of  the  muscle  during  voluntary  contraction, 
for  a  sound  is  also  heard  during  a  single  twitch  (see  first  cardiac 
sound,  page  68). 


;o2 


HUM/IN  PHYSIOLOGY 


Extensibility  of  the  tetanized  muscle.  —  The  tetanized 
muscle  is  more  extensible  than  the  resting  muscle.  The 
curve  of  its  extensibility  resembles  a  hyperbola,  but  its 
course  is  steeper  than  that  of  a  resting  muscle  (Fig.   10). 

o  10 


Fig.  io. — Curves  of  Extensibility  of  a  Resting  and  an  Active  Muscle 
(Diagrammatic). 

a,  b.  c,  d.  c.  are  the  length  of  a  resting  muscle  loaded  with  o.  10,  20.  30,  40 
grams;  the  curve  AH  which  joins  the  ends  of  these  perpendiculars  represents  the 
carve  of  extensibility.  Correspondingly,  CD  represents  the  curve  of  extensibility 
of  the  tetanized  muscle. 

Continuous  contraction  not  tetanic. — By  the  action  of  con- 
tinuous stimuli  upon  muscles  (e.g.  stimulation  by  ammonia, 
a  constant  current)  a  continuous  contraction  is  produced,  of 
which  it  has  not  been  proven  that  it  is  produced  by  the 
combination  of  twitches. 

(b)  Work  done  by  a  stimulated  muscle. — The  work  done 
is  the  product  of  the  weight  raised  by  the  height  to  which  it 
is  raised.  Other  things  being  equal,  the  height  of  the  con- 
traction is  proportional  to  the  length  of  the  fibres. 

The  force  with  which  the  weight  is  raised  is,  other  things 
being  equal,  proportional  to  the  cross-section  of  the  muscle. 
In  muscles  in  which  the  fibres  run  obliquely,  the  so-called 
physiological  cross-section,  that  is,  the  cross-section  of  all 
the  fibres,  must  be  taken  into  consideration. 

The  absolute  force  of  the  muscle  is  equivalent  to  the 
weight  which  just  prevents  the  contraction  of  a  maximal 
tetanized  muscle.      The  absolute  force  of  the  striated  frog- 


GENERAL   MUSCLE   PHYSIOLOGY  193 

muscle  is  3  kg  for  1  sq.  cm.  of  cross-section,  of  the  human 
muscle  it  is  10  kg. 

The  work  done  by  an  active  muscle  is  zero  if  the  load  is 
zero  or  if  the  load  is  so  great  that  the  muscle  can  no  longer 
raise  it.  Between  these  two  extremes  the  amount  of  work 
done  increases  with  the  increasing  load  up  to  a  certain 
maximum,  beyond  which  it  decreases. 

The  raising  of  the  load  to  a  height  equal  to  the  extent  of 
the  contraction  of  the  muscle  is  not  the  greatest  amount  of 
work  capable  of  being  performed  by  the  muscle.  The 
muscle  does  more  work  when 

(1)  The  load  is  not  raised,  but  is  thrown  upward;  it  can 
then  rise  higher  than  the  corresponding  contraction  of  the 
muscle. 

(2)  When  the  contracting  muscle  after  it  has  raised  the 
load  is  gradually  unloaded.  Then  the  muscle  shortens  more 
and  performs  new  work  by  raising  the  lessened  load.  Many 
muscles  in  the  human  body,  because  of  the  relation  of  their 
joints,  work  according  to  this  advantageous  principle  of 
unloading. 

In  addition  to  the  performing  of  real  work,  the  muscles 
also  perform  the  function  of  keeping  raised  weights  sus- 
pended and  of  holding  the  individual  parts  of  the  body 
together.  This  also  takes  place  with  expenditure  of  energy 
by  the  tension  of  the  muscles. 

An  adult  man  can  perform,  in  eight  hours,  a  work  of 
about  300,000  kilogrammetres. 

B.  The  formation  of  heat  by  active  muscles.- — Of  the 
energy  set  free  by  an  active  muscle  at  most  only  one-fourth 
is  used  for  the  performance  of  work,  the  remainder  being 
transformed  into  heat. 

The  muscles  work  much  more  economically  than  the  steam- 
engine,  for,  in  the  best-constructed  steam-engine,  only  one-tenth 
of  the  energy  set  free  by  the  burning  of  the  coal  is  used  in  doing 
work. 

When  no  external  work  is  done,  all  the  transformed  force 
appears  as  heat;   in  this  case  we  can  calculate  the  extent  of 


194  HUMAN  PHYSIOLOGY 

metabolism  by  measuring  the  heat  produced  in  the  stimulated 
muscle.  When  a  tetanized  muscle,  carrying  a  load,  holds 
the  load  suspended,  it  no  longer  does  any  work,  hence  all 
the  transformed  energy  appears  as  heat. 

To  conduct  the  experiment  in  such  a  manner  that  the  muscle 
in  acting  shall  do  no  external  work,  the  raised  weight  is  left  on 
the  muscle,  and  when  the  muscle  relaxes  it  is  allowed  to  .sink. 
The  heat  produced  by  an  excised  frog-muscle  is  measured  by  the 
thermo-electric  method,  a  delicate  thermopile  being  used.  In 
many  cases  the  heat  produced  by  a  contracting  muscle  can  be 
directlv  measured  by  a  delicate  thermometer  placed  upon  the  skin 
over  the  muscle. 

By  a  single  contraction  the  frog-muscle  increases  in  tem- 
perature by  o.ooic  to  0.0050  C,  during  tetanus  more. 
The  amount  of  heat  produced  by  the  twitching  of  a  frog- 
muscle  of  one  gram  is  about  three  micro-calories.  This 
amount  of  heat  is  produced  by  the  oxidation  of  0.0008  mg 
sugar. 

C.  Electrical  phenomena  in  the  active  muscle.  —The 
part  of  the  muscle  in  contraction  is  negative  to  the  resting 
part.  The  development  of  electricity  during  contraction 
occurs  mostly  during  the  latent  period,  so  that  the  negative 
phase  is  nearly  past  before  the  contraction  begins.  The 
wave  of  contraction  is  preceded  by  a  "  negative  wave." 

Suppose  AB  in  Fig.  11  to  be  a  muscle  fibre,  the  points 
a  and  b  of  which  are  connected  with  a  galvanometer  L.      If 

A Z ? hT B 


Fig.   11. 

we  stimulate  the  muscle  at  C,  immediately  after  the  stimula- 
tion has  reached  a  an  electric  current  passes  through  L 
from  b  to  as  a  having  become  negative.  Soon  after  this, 
when  the  stimulation  has  reached  b,  the  current  passes 
through  L  from  a  to  b.  These  currents  are  called  the 
action-currents  and   follow  each   other  with  great  rapidity. 


GENERAL   MUSCLE  PHYSIOLOGY  195 

The\*  are  investigated  with  the  same  apparatus  as  the  action- 
currents  of  nerves    see  page  217). 

Secondary  contraction,  secondary  tetanus. — If  the  nerve  of 
a  muscle-nerve  preparation  is  placed  upon  the  surface  of 
another  muscle,  and  if  the  latter  or  its  nerve  be  stimulated, 
both  muscles  are  thrown  into  simple  contraction  or  tetanus. 
The  action-current  of  the  stimulated  muscle  passes  over  into 
the  nerve  of  the  other  muscle-nerve  preparation  and  stimu- 
lates it.  Lasting  contractions,  not  of  a  tetanic  nature,  do 
not  produce  secondary  tetanus. 

If  a  muscle  is  cut  across  and  one  of  the  electrodes  of  a 
galvanometer  is  connected  with  the  transverse  section,  while 
the  other  electrode  is  connected  with  the  longitudinal  sur- 
face, a  current  passes  through  the  galvanometer  from  the 
longitudinal  to  the  cut  surface.  This  is  called  the  current 
of  rest.  At  the  cut  surface  the  muscle  dies  and  this  is  con- 
nected with  processes  which  render  the  dying  part  negative 
to  the  part  intact.  If  now  the  longitudinal  surface  is  stimu- 
lated, the  intensity  of  the  current  of  rest  is  decreased;  this 
is  called  the  negative  variation. 

The  electromotor  force  of  the  current  of  rest  of  a  muscle 
is  about  0.07  volt. 

The  cause  and  the  significance  of  these  electrical  phe- 
nomena in  stimulated  and  dying  muscles  is  not  well  under- 
stood. 


3.    THE    STIMULATION    AND    THE    IRRITABILITY    OF 
THE    MUSCLE 

The  stimulations  which  call  forth  the  activity  of  the 
muscle  may  be  divided  into : 

A.  Indirect,  i.e.  stimulations  which  act  upon  the  motor 
nerves  and  thus  upon  the  muscle.  In  this  class  belong  the 
normal  physiological  stimulations  which  are  carried  from  the 
central  nervous  system  through  the  motor  nerves  to  the 
muscles. 

B.  Direct,    i.e.     stimulations    which    affect    the    muscles 


I96  HUMAN  PHYSIOLOGY 

directly.  The  muscle  is  directly  irritable  without  the  inter- 
vention of  the  nerves,  as  is  proven  by  the  following  facts: 

(«)  In  the  sartorius  muscle  of  a  frog  the  nerve  fibres  dis- 
tribute themselves  only  in  the  middle  of  the  muscle,  for  the 
two  ends,  as  proven  by  microscopic  examination,  are  free 
of  nerve  fibres  for  about  one-eighth  of  the  total  length  of  the 
muscle.  Yet  stimulation  of  the  ends,  free  of  nerve  fibres, 
produces  contraction  of  the  muscle. 

(7;)  Ammonia  stimulates  the  muscles  directly,  but  does  not 
stimulate  the  nerve  fibres. 

(c)  Curare  paralyzes  the  nerve  endings  in  the  muscle. 
In  an  animal  poisoned  with  curare,  stimulation  of  the  nerve 
has  no  effect  upon  the  muscle,  yet  the  curarized  muscle  is 
directly  irritable. 

(<Y)  "  Idiomuscular"  contraction  is  the  local  contraction 
of  the  muscle  fibres  produced  by  the  mechanical  stimulation 
of  an  abnormal  muscle  (fatigue,  disease).  This  contraction 
is  produced  only  at  the  place  of  stimulation,  the  contraction 
not  being  spread  along  the  nerve  fibres. 

The  direct  stimuli  of  the  muscles  are: 

i.  Mechanical.  Cutting  and  pinching  of  die  muscle  stimu- 
late it. 

The  external  mechanical  conditions  also  have  an  influence 
on  the  irritability.  With  stimuli  of  the  same  strength,  the 
greater  the  resistance  which  the  contraction  of  the  muscle 
encounters,  the  more  energy  is  set  free.  This  is  useful,  for 
the  muscle  offers  more  force  against  greater  resistance. 

2.  Thermal.  Heating  above  400  produces  a  continuous 
contraction  which  finally  goes  over  into  heat  rigor  identical 
with  rigor  mortis  (see  page  198).  Below  the  temperature 
of  400,  the  irritability  increases  with  the  temperature. 

3.  Chemical.  Certain  chemical  agents  stimulate  the 
muscle,  e.g.  ammonia,  alkaline  sodium  salt  solutions;  but 
these  speedily  injure  it  so  that  it  becomes  non-irritable. 
Other  substances,  such  as  acids,  merely  injure  the  muscle 
without  previously  stimulating  it.  Physiological  salt  solu- 
tion (0.6$  NaCl)  is  indifferent. 


GENERAL   MUSCLE   PHYSIOLOGY  197 

4.  Electrical.  A  constant  current  of  sufficient  strength 
passing  through  a  muscle  in  its  longitudinal  direction  causes 
contraction  when  the  current  is  made,  and  sometimes  also 
when  the  current  is  broken.  During  the  passage  of  the 
current  through  the  muscle,  the  muscle  undergoes  a  lasting 
contraction,  which  is,  however,  less  marked  than  the  initial 
or  make  contraction. 

If  the  current  is  passed  transversely  through  the  muscle, 
it  does  not  stimulate  it. 

By  studying  the  nature  of  the  wave  of  contraction,  it  has 
been  found  that  in  the  make  contraction  the  stimulation 
begins  at  the  negative  pole  (kathode)  and  from  there  spreads 
throughout  the  muscle,  while  in  the  break  contraction  it 
begins  at  the  anode. 

Induction  currents  stimulate  only  at  the  kathode. 

In  order  to  stimulate,  the  current  must  be  active  for  a 
certain  length  of  time ;  currents  lasting  for  a  very  short  time 
are  not  effective.  The  different  kinds  of  muscles  behave 
differently  in  this  respecl .  While  striated  muscles  are  more 
affected  by  sudden  changes  in  the  intensity  than  by  long 
duration  of  the  current,  in  case  of  smooth  muscles  it  is  the 
reverse. 

At  the  places  of  entrance  and  exit  the  current  changes 

the  irritability  of  the  muscle  in  the  same  manner  as  in  the 

nerve  (see  page  220). 

The  electromotor  resistance  of  the  muscle  in  the  longitudinal 
direction  is  two  and  one-half  million,  that  in  the  transverse  direc- 
tion is  twelve  and  one-half  million,  times  greater  than  that  of 
mercury. 

Relation  between  the  stimulation  and  the  contraction. — The 
extent  of  the  contraction  (measured  by  the  heat  produced) 
increases  with  the  strength  of  stimulation  up  to  the  higher 
limit,  beyond  which  increase  in  the  stimulation  does  not 
produce  an  increase  in  contraction. 

The  irritability  of  the  muscle  is  dependent  upon  the 
normal  vital  processes,  as  well  as  upon  the  previously 
mentioned  influences  (mechanical  conditions,  temperature, 
chemical  agents,  electrical  currents). 


198  HUMAN   PHYSIOLOGY 

Excised  muscles  of  warm-blooded  animals  lose  their 
irritability  in  a  few  hours;  those  of  cold-blooded  animals,  at 
a  moderate  temperature,  in  two  to  three  days,  while  in  a 
lower  temperature  they  retain  their  irritability  for  a  long 
time  (as  long  as  twelve  days).  Stoppage  of  circulation  or 
lack  of  oxygen  soon  destroys  the  irritability  of  muscles  of 
warm-blooded  animals. 

Irritability  is  maintained  only  by  the  proper  alternate 
succession  of  rest  and  activity.  On  the  one  hand,  the 
irritability  is  lost  by  complete  rest  (e.g.  in  limbs  which 
remain  at  rest  for  a  long  time  in  fixed  bandages) ;  on  the 
other  hand,  the  irritability  is  decreased  by  too  great  stimu- 
lation. Section  of  the  motor  nerve  after  some  time  also 
destroys  the  irritability  of  the  muscles  and  causes  it  to 
degenerate. 

Fatigue  manifests  itself  by  decrease  in  irritability  and 
ability  to  do  work;  subjectively  it  manifests  itself  by  painful 
sensations  in  the  muscle.      The  fatigue  is  due  to: 

(i  )  Decomposition  products  (e.g.  sarcolactic  acid)  pro- 
duced by  the  prolonged  activity  of  the  muscle  which 
decrease  the  irritability. 

(2)   The  disappearance  of  material  for  furnishing  energy. 

If  the  fatigued  muscle  is  allowed  to  rest,  it  recovers  and 
the  irritability  increases  by  the  removal  of  the  fatigue-sub- 
stance and  by  a  fresh  supply  of  oxidizable  material. 

Rigor  mortis. — During  the  death  of  a  muscle  phenomena 
similar  to  those  of  a  contracting  muscle  appear,  namely, 
contraction  (produced  by  the  tension  of  the  muscle  in  rigor 
mortis),  production  of  heat,  consumption  of  oxygen,  forma- 
tion of  carbon  dioxide  and  lactic  acid,  disappearance  of 
glycogen,  electrical  phenomena.  Rigor  mortis  has  there- 
fore been  regarded  as  the  last  contraction  of  the  dying 
muscle. 

Besides  the  above-named  processes,  the  coagulation  of 
myosinogen  also  takes  place;  this  causes  the  dead  muscle 
to  have  a  whitish,  cloudy  appearance. 

The  nervous  system  influences  ricror  mortis.     Rigor  mortis 


GENERAL   MUSCLE  PHYSIOLOGY  199 

sets  in  later  in  a  muscle  whose  motor  nerve  has  been  cut 
than  in  a  muscle  whose  nerve  has  not  been  cut. 

Heat  rigor,  which  takes  place  when  a  muscle  is  killed  by 
heating  it  above  40°  C,  is  identical  with  rigor  mortis. 

Physiological  differences  between  smooth  and  striated 
muscles. — The  smooth  muscles  differ  physiologically  from 
the  striated  in  the  following  points : 

1.  The  striated,  except  the  cardiac  muscles,  are  voluntary 
muscles;  the  smooth,  except  the  ciliary  muscles  of  the  eye 
which  function  during  accommodation,  are  involuntary. 

2.  The  smooth  muscles  contract  more  slowly  and  the 
contraction  wave  is  much  longer  than  in  the  striated  muscles 
(see  page  190).  Of  the  striated  muscles, the  cardiac  muscle 
contracts  more  slowly  than  the  skeletal  muscles.  But  in 
the  cardiac  muscle  the  striation  is  less  perfect  than  in  skeletal 
muscles.  The  more  nearly  perfect  the  cross-striation  the 
greater  the  velocity  of  contraction. 

3.  Smooth  muscles  are  more  readily  stimulated  by  long 
duration  than  by  sudden  changes  in  the  intensity  of  the 
electric  current,  while  the  striated  muscles  are  more  readily 
stimulated  by  sudden  changes  in  the  intensity  of  the  current. 

4.  In  the  smooth  muscle  the  stimulation  passes  from  one 
fibre-cell  to  another,  not  so  in  the  striated  muscle  (except 
cardiac). 

Protoplasmic  and  ciliary  movement. 

I.  Protoplasmic  movement. — White  blood  corpuscles,  like 
amceba,  change  their  shape  by  the  thrusting  out  and  draw- 
ing in  of  pseudopods.  By  attaching  a  pseudopod  to  the 
underlying  surface  and  drawing  the  body  along  by  the  con- 
traction of  the  protoplasm,  they  are  also  able  to  move  from 
place  to  place.  During  rest  the  pseudopods  are  withdrawn 
and  the  cell  is  spherical. 

Within  the  limits  of  temperatures  by  which  the  cell  is  not 
injured,  the  higher  the  temperature  the  greater  the  proto- 
plasmic movements.  At  a  temperature  of  a  little  above 
400  C.  the  pseudopods  are  withdrawn  ;  in  heat  rigor  the 
cell  is  spherical.      Lack  of  oxygen  paralyzes. 


200  HUMAN  PHYSIOLOGY 

If  the  cells  are  stimulated   by  an   induction   current,    the 

pseudopods  are  withdrawn.      Stimulations  which  work  upon 

the  cell  from  one  side,  e.g.  chemical    influences,  may  have 

an  orientating  effect  upon  the   movements  of  the  cell.      The 

wandering  of  the  leucocytes  through  the  walls  of  the  blcod 

vessels    into    the    tissues    seems   to    be   caused   by   chemical 

stimulation  falling  upon  the  cell  from  one  side  only. 

The  constant  electric  current  also  orientates  the  movements  of 
naked  protoplasmic  bodies,  by  polarization  at  the  places  of 
entrance  and  exit.  In  many  amoebae  the  movements  are  always 
towards  the  kathode.  The  orientating  effects  of  chemical  and 
electric  stimulations  are  called  chematropism  and  galvanotropism. 

2.  Ciliary  movements. — The  epithelial  cells  of  many 
mucous  membranes  have,  on  their  free  surfaces,  cilia  which 
move  forward  and  backward  in  a  definite  direction.  The 
movement  in  one  direction  takes  place  with  greater  velocity 
than  in  the  opposite  direction,  hence  light  particles  resting 
on  the  surface  of  the  mucous  membrane  are  carried  forward 
in  that  direction  in  which  the  movement  is  stronger. 

The  ciliated  epithelial  cells  of  a  mucous  membrane  stand 
in  close  physiological  relation  to  each  other,  so  that  the 
movements  of  all  the  cilia  occur  in  a  definite,  orderly 
manner.  The  nature  of  this  physiological  relationship  is 
not  known. 

The  activity  of  the  cilia  is  favored  by  oxygen  and  by  the 
feeble  alkalinity  of  the  surrounding  fluid. 

In  man,  cilia  are  found  in  the  mucous  membrane  of  the 
air  passages,  uterus,  oviducts,  and  on  the  ependyma  of  the 
cerebral  ventricles.  The  movements  of  the  cilia  in  the  air 
passages  force  the  mucous  and  the  inhaled  dust  outward;  the 
movements  of  the  cilia  in  the  oviducts  and  uterus  serve  to 
move  the  e^g  forward. 

The  spermatozoa  are  composed  of  a  head  and  a  long 
thread-like  tail.  This  tail,  by  making  whiplike  or  pendu- 
latory  movements  (analogous  to  the  cilia  of  the  ciliated  cells), 
propels  the  spermatozoa  forward.  These  movements  are 
increased  by  the  feeble  alkalinity  of  the  medium  in  which 
the  spermatozoa  move  ;   they  are  decreased  by  acid  fluids. 


CHAPTER    XV 
SPECIAL   PHYSIOLOGY   OF   THE    MUSCLES 

THE  subjects  of  the  special  physiology  of  the  muscles  are: 

1.  The  functions  of  the  skeletal  muscles  in  general. 

2.  Standing,  walking,  and  running. 

3.  The  voice. 

1.    FUNCTIONS    OF    THF    SKELETAL    MUSCLES    IN 
GENERAL 

A.  The  bones  and  their  articulations. — The  bones  are 
rigid  bodies  which  support  the  various  soft  parts  of  the 
animal  body.  They  are  formed 
so  as  to  furnish  the  greatest 
strength  with  the  least  bulk.  To 
accomplish  this  the  long  bones 
are  hollow,  and  in  the  short  bones 
the  lamellae  are  especially  closely 
packed  in  the  direction  in  which 
the  greatest  pressure  or  pull  is 
exerted  (see  Fig.   12). 

The  articulations  may  be    di- 
vided into : 

1.   Synchondrosis,  the  articu- 
lation of  two  bones  by  means  of 

cartilage.      In  synchondrosis,  the  T, 

fa  J  Fig.     12. — Liter   Part  of  the 

bones  retain,    when   no   external      Femur,  showing  the  arrange- 

forces  are  active,  a  definite  posi-      ^nt  of  the  Lamell^. 

r  (After  H.  Meyer.) 

tion    towards    each    other;     when       The  lamella  are  especially  closely 
external   forces  are  applied,    the  packed  in  the  direction  in  which 

the  weight    of   the    body    acts  and 
bones  Can  move   upon  each  Other  in  which  the  muscles  inserted  upon 

in    all    directions,    the    cartilage  the  trochanter  major  act. 
being  twisted.      Such  movement  is,  however,  very  limited. 

201 


202  HUMAN  PHYSIOLOGY 

2.  Joints,  i.e.  articulation  without  definite  position  of 
equilibrium  of  the  articulated  bones. 

The  two  surfaces  by  which  the  two  bones  are  jointed  touch 
each  other ;  the}'  are  smooth  and  can  move  over  each  other, 
and  this  movement  is  aided  by  the  synovia,  a  fluid  found  in 
the  joints  which  acts  as  a  lubricant. 

Synovia  is  an  alkaline  stringy  fluid  which  is  rendered  cloudy  by 
the  remains  of  cells.  It  contains  proteids,  salts,  and  a  nucleo- 
albumin  which  is  similar  to  but  not  identical  with  mucin.  Its 
composition  varies  with  rest  and  activity. 

Frequently  there  is  found  between  the  two  bones  of  the 
joint  a  cartilage  which  serves  to  give  greater  surface  to  the 
joint  and  aids  in  the  movement  of  the  bones  in  cases  where 
the  two  heads  of  the  bones  do  not  fit  into  each  other. 

The  joints  are  covered  by  the  capsular  membrane.  This 
is  a  connective  tissue  membrane  fastened  to  the  bones  which, 
by  its  flaccidity,  allows  the  movements  of  the  bones  against 
each  other. 

Many  joints,  amphiartrosis,  have  a  membrane  so  tense  that  no 
movement  of  the  bones  is  possible.  These  joints  are,  from  a 
mechanical  standpoint,  equivalent  to  the  synchondroses. 

The  surfaces  of  the  joint  are  planes  of  rotation.  A  plane 
of  rotation  is  a  plane  described  by  a  curve  when  it  is  rotated 
around  a  straight  line  lying  in  the  plane  of  the  curve. 

The  joints  are  classified  according  to  the  form  of  the 
curve  describing  the  plane  of  rotation  and  the  position  of  the 
axis  of  rotation. 

I.    The  curve  is  the  arc  of  a  circle. 

{a)  The  straight  line  passes  through  the  centre  of  the 
circle.  The  plane  of  rotation  is  a  part  of  a  spherical  surface. 
A  joint  with  such  planes  is  called  a  ball-and-socket  joint, 
or  arthrodia.  In  such  a  joint  the  jointed  bones  turn  around 
any  number  of  axes  of  rotation  which  all  pass  through  the 
centre  of  the  sphere.  We  may,  however,  conceive  of  all 
the  possible  movements  as  movements  around  three  lines 
perpendicular  to  each  other  and  passing  through  the  centre 
of  the  sphere.      Examples:   hip-joint,  shoulder-joint. 


SPECIAL    PHYSIOLOGY   OF   THE   MUSCLES.  203 

(<£)  The  straight  line  docs  not  pass  through  the  centre 
of  the  circle. 

(a)  It  lies  on  the  concave  side  of  the  arc :  oval  plane, 
oval  joint. 

The  oval  joint  has  two  axes,  of  which  one  coincides  with 
the  rotation  axis  of  the  plane  of  rotation ;  the  other,  passing 
through  the  centre  of  the  arc,  is  perpendicular  to  the  first 
axis.      Example:    radio-carpal  joint. 

(/&)  The  straight  line  lies  on  the  convex  side  of  the  arc : 
saddle-joint. 

The  saddle-joint  has  two  axes  which  are  analogous  to 
those  of  the  oval  joint.  Example:  joint  between  the  trape- 
zium and  the  metacarpus  pollicis. 

2.  The  curve  has  any  form  except  that  of  a  circle,  and 
the  straight  line  may  have  any  position. 

Such  joints  are  called  hinge  joints;  they  have  one  axis  of 
rotation  which  coincides  with  the  axis  of  the  plane  of  rota- 
tion. If  one  of  the  two  bones  forming  a  hinge-joint  is 
imagined  to  be  fixed,  a  given  point  of  the  second  bone, 
on  moving,  describes  a  circle.  Example:  joints  of  the 
phalanges. 

As  special  cases  we  must  also  mention : 

1 .  The  screwed-surface  joint,  a  joint  with  nne  axis  and  in 
which  a  given  point  of  the  supposed  movable  bone  describes 
a  spiral  line  instead  of  a  circle.  In  the  screwed-surface  joint 
the  bones,  during  turning,  slide  over  each  other  in  opposite 
directions  but  move  in  the  direction  of  the  axis.  Example: 
the  elbow. 

2.  The  spiral  joint.  The  plane  of  rotation  of  the  spiral 
joint  may  be  conceived  of  as  follows:  The  curve  which  by 
its  rotation  describes  the  plane  of  rotation  approaches  during 
this  movement  nearer  to  the  straight  line.  A  given  point 
in  the  curve,  therefore,  does  not  describe  a  circle  but  a 
spiral.  Hence  a  given  point  of  the  imaginary  movable  bone 
describes  not  a  circle  but  a  spiral.      Example:   the  knee. 

Mechanisms  by  which  the  joints  are  held  together. — Besides 
the  ligaments  (ligamenta  accessoria  of  the  hinge-jointj  and 


204  HUMAN   PHYSIOLOGY 

the  tension  of  the  surrounding    muscles,    the  bones  of  the 
joints  are  held  together  by  atmospheric  pressure. 

If,  in  a  dead  body,  all  the  connections  between  the  femur 
and  the  pelvis  are  cut,  and  also  the  capsular  membrane  of 
the  hip-joint,  the  femur  still  remains  in  its  socket  because 
atmospheric  pressure  presses  the  surfaces  of  the  joint  against 
each  other.  The  force  with  which  the  bones  are  held 
together  by  atmospheric  pressure  is,  in  the  hip-joint,  about 
22  kg,  which  is  more  than  the  weight  of  the  limb. 

Limitations  in  the  movements  of  bones  connected  by  joints. 
— The  movements  of  the  bones  are  naturally  limited,  often 
especially  so  by  processes  of  the  bone  (e.g.  the  olecranon 
process,  which  prevents  the  complete  rotation  of  the  elbow 
forward)  and  by  ligaments  (e.g.  the  posterior  crucial  liga- 
ment of  the  knee,  which  prevents  the  complete  backward 
bend  of  the  knee). 

B.  Action  of  the  muscles  upon  the  bones. — By  the  con- 
traction of  a  muscle  its  points  of  insertion  are  brought  nearer 
together.  Hence  a  muscle  can  only  act  when  its  points  of 
insertion  can  approach  each  other. 

But  the  line  in  which  the  insertion  points  approach  each 
other  does  not  always  coincide  with  the  longitudinal  direc- 
tion of  the  muscle  fibres,  because  the  insertion  points  are 
not  free  to  approach  each  other  in  a  straight  line,  but  the 
nature  of  their  movement  is  determined  by  the  nature  of  the 
articulation. 

If,  for  example,  the  two  insertion  points  are  attached  to  two 
bones  articulated  by  ball-and-socket  joint,  and  if  we  imagine  one 
bone  as  immovable,  then  the  insertion  point  on  the  other  bone 
can  only  assume  points  all  of  which  lie  in  a  spherical  plane.  If 
the  bones  are  articulated  by  a  hinge-joint,  the  insertion  joint  on 
the  imaginary  movable  bone  can  move  only  in  a  circle. 

By  the  contraction  the  insertion  points  approach  each 
other  because  the  muscle  fibres  are  stretched  straight 
between  the  insertion  points. 

If  the  muscle  fibres  are  not  stretched  straight  between  the  inser- 
tion points  but  move  over  a  pulley-like  arrangement,  the  points. 


SPECIAL    PHYSIOLOGY   OF   THE  MUSCLES 


205 


of  insertion  can,  by  the  contraction  of  the  muscle,  go  farther 
apart.  This  is  the  case,  e.g.,  in  the  superior  oblique  muscle, 
whose  insertion  on  the  eyeball  is  removed  by  the  contraction  of 
the  muscle  from  its  insertion  in  the  optic  foramen,  because  the 
trochlea  serves  as  a  pulley. 

All  the  force  of  a  contracting  muscle  is  effective  for 
mechanical  work  only  when  the  insertion  points  move  in  the 
longitudinal  direction  of  the  fibres.  In  all  other  cases  only 
a  part  of  the  muscle  force  is  effective.  This  part  is  found 
by  resolving  the  force  into  its  components  according  to  the 
law  of  the  parallelogram  of  forces. 

Example, — In  Fig.  13,  let  AB  and  AC  be  two  bones  which  by 
the  hinge-joint  A  move  around  a  line  passing 
through  A  perpendicular  to  the  plane  of  the 
paper.  /  and  J1  are  the  insertion  points  of  a 
muscle  fibre  m,  by  the  contraction  of  which 
the  point  /,  is  moved  forward  in  the  direction 
perpendicular  to  AC  (J  is  supposed  to  be 
immovable).  If  the  force  of  the  muscle  is 
represented  by  the  length  of  the  line  JVD,  that 
part  of  the  force  which  causes  /j  to  move 
iorward  is  found  by  resolving  JXD  into  its 
components.  According  to  the  law  of  the 
parallelogram  of  forces,  draw  JxE  and  its  per- 
pendicular LF.  JxE  indicates  the  amount  of 
force  which  causes  f  to  move  forward. 

If,  in  a  hinge-joint,  the  direction  of  pull  of 
a  muscle  acting  upon  a  given  point  of  the 
movable  bone  does  not  fall  in  the  plane  of 
the  circle  described  by  the  moving  point,  the 
muscle  force  must  be  resolved  into  three  com- 
ponents. One  of  these,  the  active  component, 
falls  in  the  direction  of  the  moving  point,  the  other  two,  inactive, 
are  perpendicular  to  this  and  also  to  each  other,  and  one  of  these 
lies  in  the  plane  of  the  circle. 

In  a  ball-and-socket  joint  the  muscle  force  is  resolved  into  two 
components  whose  directions  fall  in  the  plane  of  traction  of  the 
muscles  and  the  centre  of  the  ball.  One  of  these  components, 
the  active,  lies  in  the  direction  in  which  the  supposed  movable 
insertion  point  moves  in  this  plane;  the  other  is  perpendicular  to 
this. 

If  two  or  more  muscles  work  upon  a  movable  bone,  we 
first  determine  the  active  component  of  each  force,  and  of 


Fig. 


206  HUM4N  PHYSIOLOGY 

these  individual  active  components  we  find  the  single  result- 
ant according  to  the  law  of  the  parallelogram  of  forces. 

Muscles  acting  in  the  same  direction  are  said  to  be  syner- 
getic,  while  antagonistic  muscles  are  those  which  act  upon  a 
joint  in  opposite  directions. 

We  may  analyze  the  movements  of  the  bones  according 
to  the  laws  of  the  lever,  for  all  movable  bones  may  be  con- 
sidered as  one-  or  two-armed  levers.  The  length  of  the 
lever-arms  from  force  to  fulcrum  and  that  from  fulcrum  to 
weight  is  the  distance  from  the  axis  of  the  joint  to  the  point 
at  which  the  force  and  the  weight  work. 

In  the  body,  the  lever-arm  of  the  force  is  generally  smaller 
than  that  of  the  weight.  This  is  not  unfavorable,  however, 
for  by  it  we  gain  velocity,  even  though  it  be  at  the  expense 
of  force. 

During  the  motion  of  the  supposed  movable  bone,  the 
amount  of  the  effective  force  frequently  changes  because  of 
changes  in  the  lever-arm  either  of  the  force  or  of  the  weight. 

(  )f  interest  is  the  decrease  of  the  weight-arm  during  the  move- 
ment, for  thereby  the  muscle  works  more  advantageously  (see  page 
193).  An  example  of  a  movement  of  the  body  during  the  unload- 
ing [Entlastung]  of  a  muscle  is  the  elevating  of  the  body  by  the 
knee-joint.  In  the  position  with  flexed  knee,  the  lever-arm  of  the 
weight  is  the  horizontal  distance  of  the  axis  of  the  knee-joint  from 
the  perpendicular  line  through  the  centre  of  gravity  of  the  body, 
which  lies  at  the  promontorium.  This  distance  becomes  smaller 
as  the  body  is  elevated  and,  in  the  upright  position,  is  zero.  The 
direction  of  pull  of  the  quadriceps,  which  straightens  the  knee, 
retains,  during  the  movement,  approximately  the  same  distance 
from  the  axis  of  the  knee-joint. 

2,   STANDING,    WALKING,    RUNNING 

The  general  erect  position  (standing)  and  the  general 
modes  of  locomotion  (walking,  running)  have  a  typical  form 
in  all  people,  for  they  are  based  upon  a  common  principle, 
that  of  the  least  muscular  exertion.  We  are  accustomed  so 
to  stand  and  move  that  the  muscles  are  as  little  exerted  as 
possible. 


SPECIAL   PHYSIOLOGY   OF    THE   MUSCLES  207 

In  standing  erect  the  position  of  the  body  is  such  that  the 
centre  of  gravity  is  vertically  over  the  base  formed  by  the 
feet,  and  when  the  limbs  are  placed  against  each  other,  the 
longitudinal  axis  of  the  bod}'  is  nearly  vertical. 

The  base  of  support  is  a  hexagon  whose  angles  are  formed 
by  the  heads  of  the  first  and  fifth  metatarsus  and  by  the 
calcaneum  on  both  sides.  The  centre  of  gravity  of  the  body 
lies  somewhat  in  front  of  the  promontorium  of  the  spinal 
column. 

The  muscles  which  during  quiet  standing  fix  the  limb  are, 
in  reality,  only: 

1.  Calf-muscles.  The  contraction  of  these  prevents  the 
body  from  falling  forward  which  might  be  caused  by  the 
bending  of  the  lower  part  of  the  leg  at  the  ankle-joint. 

2.  The  muscles  of  the  neck,  by  the  contraction  of  which 
the  forward  sinking  of  the  head  is  prevented  (lowering  of  the 
chin  upon  the  chest  as  in  sleep). 

3.  To  a  smaller  degree  the  neck  and  hip  muscles,  which 
prevent  the  bending  of  the  cervical  and  lumbar  vertebrae. 

Besides  this  the  limbs  are  held  firm  by  the  following 
ligaments : 

(1)  The  superior  ileo-femoral  ligaments  fligamenta  Ber- 
tini)  which  prevent  the  body  from  falling  backward  by  turn- 
ing at  the  hip-joints. 

(2)  The  posterior  crucial  ligaments  of  the  knee-joints, 
which  prevent  the  body  and  the  upper  part  of  the  legs  from 
falling  forward  by  turning  at  the  knee-joints. 

As  the  arms  hang  loosely  suspended  by  the  sides  of  the 
body,  they  need  no  mechanism  for  fixation. 

Many  authors  suppose  that  the  body  is  not  thrown  forward  but 
backward  by  the  bending  of  the  knees.  If  this  is  true,  the  fixation 
of  the  knees  is  not  caused  by  the  posterior  crucial  ligaments,  but 
by  the  quadriceps  femoris. 

Turning  the  feet  out  aids  in  holding  the  lower  limb  against  the 
foot  in  the  ankle,  for  in  placing  the  feet  outward  the  two  axes  of 
the  joints  do  not  fall  in  the  same  direction  but  converge  forward. 
This  makes  a  simultaneous  rotation  around  both  axes,  without  a 
change  in  the  position  of  the  legs,  impossible. 


2o8  HUMAN  PHYSIOLOGY 

Locomotion. — In  locomotion,  the  head,  the  trunk,  and  the 
suspended  arms  must  be  regarded  as  a  body  balanced  upon 
the  legs  at  the  hip-joints.  The  legs  support  the  body  and, 
by  stretching,  push  it  forward.  The  leg  can  swing  forward 
and  backward  without  any  muscular  exertion.  In  order 
that  the  one  leg  may  swing  forward,  it  is  somewhat  elevated 
by  a  slight  bending  at  the  hip-,  knee-,  and  ankle-joints;  the 
bod\'  is  meanwhile  supported  by  the  other  leg.' 

The  top  part  of  the  body  is  slightly  bent  forward  during 
locomotion;  this  is  the  greater  the  faster  the  motion.  The 
forward  movement  of  the  body  is  produced  by  the  alternate 
action  of  one  leg  supporting  the  body  and  pushing  it  forward 
while  the  other,  slightly  bent,  swings  forward. 

In  walking,  a  period  during  which  both  feet  are  on  the 
ground  is  followed  by  a  period  in  which  only  one  is  placed 
on  the  ground  while  the  other  swings.  In  running,  a  period 
during  which  neither  foot  rests  on  the  ground  is  followed  by 
a  period  during  which  one  stands  while  the  other  swings. 

The  process  from  the  beginning  of  the  swinging  of  one 
leg  until  the  beginning  of  the  swinging  of  the  other  is  called 
a  step.  The  velocity  of  locomotion  is  the  greater  the 
longer  the  step  and  the  greater  the  number  taken  in  a  given 
time  (or  the  smaller  the  duration  of  the  step).  The  velocity 
of  locomotion  during  walking  is  limited — maximum  2.5  m 
per  second — because,  on  account  of  the  simultaneous  resting 
of  both  feet  on  the  ground,  the  length  and  number  of  the 
steps  cannot  exceed  a  certain  amount.  In  running,  the 
velocity  of  motion  can  be  greater  than  in  walking  because 
the  length  and  number  of  steps  can  be  increased,  on  account 
of  the  simultaneous  swinging  of  both  feet. 

In  walking,  the  velocity  is  the  greater  the  lower  the 
position  of  the  head  of  the  femur.  Synchronously  with  the 
movements  of  the  legs,  a  rhythmical  pendulation  of  the  arms 
takes  place,  in  opposite  direction  to  that  of  the  legs. 

The  alternate  rising  and  sinking  of  the  body  during  walk- 
ing is  small  (about  32  mm). 

The  work   done  by  the   body  during  walking  on   a  hori- 


SPECIAL    PHYSIOLOGY   OF   THE   MUSCLES 


209 


zontal  plane  is  about  3  kilogrammetres  for  each  step ;  during 
running  it  is  more.  This  work  is,  however,  not  lasting, 
since,  during  each  step,  the  elevation  of  the  body  is  lost. 


3.    VOICE    AND    SPEECH 

1.  Production  of  voice. — The  larynx  with  the  vocal 
cords  forms  a  reed  organ  with  membranous  reeds.  During 
the  production  of  voice  the  inner  borders  of  the  vocal  cords 
approach  each  other  and  are  stretched.  When,  now,  the 
expired  air  passes  through  the  larynx,  the  vocal  cords 
vibrate.  By  this  vibration  of  the  cords,  the  glottis  alter- 
nately opens  and  closes  so  that  the  expired  air  is  emitted 
intermittently.  In  this  manner,  vibrations  of  the  air  are 
produced  which  are  strengthened  by  the  resonance  of  the 
pharynx  and  mouth  and  can  be  perceived  as  sounds  by  the 
ear. 

(«)   The  mechanism  of  the  vocal  chords. — The  cartilages 
concerned  in  the  study  of  the  vocal 
cords  are : 

The  cricoid,  a  cartilaginous  ring 
at  the  upper  part  of  the  tracheal 
wall ;  it  has  the  form  of  a  signet 
ring  with  the  broad  part  on  the 
posterior  side  fcr,  Fig.   14). 

2.  The  thyroid  fth)  consists  of 
two  perpendicular  plates  which 
meet  at  a  right  angle  in  front ;  the 
posterior  border  is  continued  up- 
ward as  the  large  horn,    and  down-    ,    ^thyroid  cartilage;  a.anaUer 

&  horn  01    the    thyroid  cartilage; 

ward    as    the    small    horn    fa).       The     or,    arytenoid  ;      m,     processus 
^^:.,<-       fit  Hi  c     '       ■    •    ,        muscularis  ;     r,  processus  voca- 

points  of  the  small  horns  form  joints    lis .   cA>  vJcai'cphords;  cr>  cri. 
with  the  sides  of  the  cricoid.      The    coid;  b~b  ■>  direction  of  move- 

r   , ,  .       .    .    J  .       ,  .    ,       ,         ment  of   the    thyroid    cartilage 

axis  of  this  joint  around  which  the    during  contraction  of  the  crico- 
thyroid    turns    is    horizontal    from    thyroid  (M.  eric.  thyr.). 
right  to  left. 

3.  The    arytenoids    far)    are    two    three-sided    pyramids 


eric.  thyr. 


Fig.   14. — Profile  of  the 
Larynx. 


HUMAN  PHYSIOLOGY 


whose  bases  are  movably  articulated  with  the  posterior  parts 
of  the  upper  surface  of  the  cricoid. 

The  vocal  cords  are  foldlike  processes  of  the  inner  wall 
of  the  larynx,  which  in  front  are  attached  to  the  posterior 
wall  of  the  thyroid  ;  at  the  rear  they  are  attached  to  the  vocal 
processes,  which  are  anterior  processes  of  the  triangular 
bases  of  the  arytenoids.  During-  quiet  breathing  the  space 
between  the  vocal  cords  and  the  two  arytenoids,  called  the 
glottis,  is  open.  The  glottis  has  the  form  of  an  isosceles 
triangle  (Fig.  16,  I).  When  the  glottis,  for  production  of 
voice,  must  be  narrowed,  the  arytenoids  approach  each 
other  until  they  come  into  contact  and  the  vocal  cords  are 
tense. 

A.  In  the  closing  of  the  glottis,  the  following  parts  func- 
tion : 

i .  The  transverse  and  oblique  arytenoid  muscles,  which  are 
inserted  on  the  posterior  side  of  the  two  arytenoids  and  by 
their  contraction  draw  the  posterior  parts  of  the  arytenoids 
toward  the  median  line  (Figs.    15  and  16,  II  and  III). 

2.    The   lateral  crico- arytenoid  on  both   sides,  which  pro- 
ceeds  from    the    lateral  surface  of  the   cricoid   upward    and 
ryt.tr.et  obi.         backward  to  the  muscular  pro- 
cesses (lateral  angle  of  the  base 
of  the  arytenoids).     By  the  con- 
traction    of    the     muscles     the 
arytenoids    are    turned   about   a 
vertical  axis  and  the  vocal  pro- 
cesses   are    drawn    toward    the 
median   line.      Its   antagonist  is 
the     posterior     crico- arytenoid, 
which     alone    turns    the    vocal 
muscle.  processes   outward  and,  in  con- 

junction with  the  lateral,  turns  the  whole  arytenoid  outward. 
In  this  manner  the  glottis  is  opened. 

B.  To  rentier  the  vocal  cords  tense,  the  following  parts, 
function  : 

1.     The    crico-thyroid    muscle,    which    pulls    the    thyroid 


-31.  eric.  ary.  post 


Fig.  15. 


-Posterior  View  of 
Larynx. 
M.  arvt.  Ir.  ii  obi.,  transverse  and 
oblique  arytenoid  muscles;   M.   eric. 
ary.    post.,    posterior  cricoarytenoid 


SPECIAL    PHYSIOLOGY   OF    THE   MUSCLES 


forward  and  a  little  downward  and  hence  increases  the  ten- 
sion of  the  vocal  cords  attached  to  the  thyroid. 

2.  The  thyro-arytenoid  muscle,  imbedded  in  the  vocal 
cords,  function  as  the  antagonist  of  the  last-named  muscle. 
If  it  contracts  simultaneously  with  the  crico-thyroid  muscle, 
both  it  and  the  vocal  cords  which  are  formed  by  it  are 
rendered  tense.  Its  contraction  also  aids  in  the -closing  of 
the  glottis,  for  the  slightly  outward-bent  borders  of  the 
vocal  cords  are  stretched  by  its  contraction. 

Innervation :  The  crico-thyroid  is  innervated  by  the 
superior  laryngeal  nerve ;  all  the  others  by  the  inferior 
laryngeal. 


^J\? 


IV. 
the  Vocal  Cords 


I.  II.  HI. 

Fig."  1 6. — Representation  of  the  Position 
(  d i agr  amm  atic). 
a,  anterior  end  of  the  vocal  cord;  £  and  c,  base  of  the  arytenoid  cartilages; 
I,  position  of  rest;  II,  the  arytenoid  have  approached  each  other  and  the  vocal 
cords  are  in  position  for  voice  formation;  III,  form  of  the  glottis  during  con- 
traction of  the  transverse  and  oblique  arytenoid  muscles  and  the  posterior 
crico-arytenoid;  IV,  form  of  the  glottis  during  contraction  of  the  lateral  crico- 
arytenoid muscles. 

(b)  The  pitch,  range,  and  quality  {timbre)  of  the  human 
voice. — The  pitch  of  a  reed  pipe  depends  on  the  number  of 
vibrations  of  the  reed.  In  a  membranous  reed,  it  depends- 
upon  the  length,  thickness,  and  tension  of  the  reed,  hence 
the  pitch  of  the  human  voice  is  the  higher  the  less  the 
length  and  thickness  and  the  greater  the  tension  of  the 
vibrating  parts  of  the  vocal  cords. 

Individual  variations  in  the  pitch  of  the  voice  are  deter- 
mined by  the  length  and  thickness  of  the  vocal  cords.  The 
vocal  cords  of  a  man,  for  example,  are  thicker  and  longer 
(18  mm  long)  than  those  of  a  woman  (12  mm  long),  hence 
the  man  has  a  deeper  voice  than  the  woman. 


212  HUMAN  PHYSIOLOGY 

Children  do  not  show  this  difference  in  voice.  The  change  of 
the  voice  in  man  takes  place  at  puberty.  Castration  prevents  this 
change. 

One  and  the  same  individual  produces  tones  of  various 
pitch  by: 

(i)  Changes  in  the  tension  of  the  vocal  cords,  produced 
by: 

(a)  Changes  in  the  contraction  of  the  muscles  which 
cause  the  tension  of  the  cords  to  vary. 

(J?)  By  changes  in  the  force  with  which  expired  air  is 
emitted. 

If  the  air  is  exhaled  forcibly,  the  vocal  cords  are  brought 
into  a  new  and  slightly  raised  position  which  produces  a 
greater  tension  than  when  they  are  stretched  straight 
between  their  points  of  insertion. 

The  force  of  the  exhaled  air  is  generally  I  3— 1 7  mm  Hg. 

(2)  Variations  in  the  length  and  breadth  of  the  vibrating 
parts  of  the  vocal  cords. 

(a)  Variation  in  the  length  of  the  vibrating  part  is  pro- 
duced by  the  greater  or  less  pressing  together  of  the  aryte- 
noids. If  these  are  loosely  pressed  together,  the  edges  of 
the  arytenoids  also  vibrate,  but  if  the}-  are  firmly  held,  the 
vocal  cords  only  vibrate.  In  the  first  case  the  vibrating 
reed  is  longer  than  in  the  second  case. 

(/>)  By  peculiarities  in  the  contraction  of  the  thyroaryte- 
noid muscle  or  by  the  so-called  false  vocal  cords  being 
placed  upon  the  true  vocal  cords  so  that  only  the  small 
inner  margins  of  the  true  cords  are  allowed  to  vibrate.  Be- 
cause of  the  small  extent  of  the  vibrating  part,  the  pitch  is 
high.      It  is  used  in  the  so-called  falsetto. 

(3)  Variations  in  the  thickness  of  the  vocal  cords. 

Fibres  of  the  thyro-arytenoid  muscle,  having  a  perpendic- 
ular direction,  by  their  contraction  cause  the  upper  and 
lower  surfaces  of  the  vocal  cords  to  approach  each  other  and 
thus  change  their  thickness. 

The  range  of  the  voice  includes  all  the  tones  which  an 
individual  can  produce;  generally  it  embraces  two  octaves. 


SPECIAL    PHYSIOLOGY   OF   THE  MUSCLES  213 

The  range  of  the  voice  varies  in  different  individuals.      We 
may  classify  them  as: 

Base,  ranges  from  E  to  f '. 
Tenor,  ranges  from  c  to  c" . 
Alto,  ranges  from  f  to  f" . 
Soprano,  ranges  from  c'  to  c'" . 

The  timbre  of  the  voice  depends  upon  the  number  and 
strength  of  the  overtones  which  accompany  the  fundamental 
tone  produced  in  the  larynx.  It  is  also  dependent  upon 
accompanying  noises.  In  one  and  the  same  individual  we 
can  distinguish,  by  means  of  the  timbre,  the  chest-tone  from 
the  falsetto.  The  resonance  of  the  chest-tone  is  chiefly 
produced  in  the  thorax  and  is  deeper ;  the  resonance  of  the 
falsetto  is  chiefly  produced  in  the  mouth,  pharynx,  and  nose, 
and  is  higher.  The  resonance  only  affects  the  timbre  and 
strength,  not  the  pitch,  of  the  voice. 

The  difference  between  the  voice  during  singing  and 
speaking  is  not  fully  understood. 

2.  Speech. — The  sounds  of  speech  are  produced  by  ex- 
piration, which  causes  noises  to  be  produced  in  the  mouth 
or  nose  and  in  the  pharynx.  These  sounds  may  or  may 
not  be  accompanied  by  the  voice. 

Vowels  are  sounds  of  speech  accompanied  by  the  voice. 
The  tones  which,  produced  in  the  buccal  and  pharyngeal 
cavities,  accompany  the  voice  to  give  to  it  the  vowel  char- 
acter, are  called  the  determinants  [Formanten]  of  the  vowels. 

Each  vowel  has  one  or  two  characteristic  determinants 
which  are  independent  of  the  pitch  of  the  voice.  These  are, 
according  to  Helmholtz :  for  00  as  in  food,  f;  for  o  as  in  no,  b' ; 
for  a  as  in  father,  b"  \  for  a  as  in  ate,  f  or  b'" ;  for  e  as  in 
scheme,  f  and  d"".      Other  authors  give  other  determinants. 

In  the  several  vowels  the  determinants  are  different 
because  of  the  difference  in  the  position  of  the  buccal  and 
pharyngeal  cavities.  For  the  production  of  a  as  in  father, 
the  cavity  of  mouth  and  pharynx  has  the  shape  of  a  funnel 
with  the  apex  toward  the  pharynx ;   for  the  production  of  o 


214  HUM/IN  PHYSIOLOGY 

as  in  //<•>,  and  oo  as  in  food,  it  has  the  form  of  a  flask  with  a 
short  neck  ;  while  for  the  production  of  a  as  in  ate,  and  e 
as  in  scheme,  it  has  the  form  of  a  flask  with  a  long  neck. 

Perhaps  there  are,  in  the  formation  of  vowels,  besides  these 
definite  determinants,  others  which  are  produced  by  the 
resonance  of  the  buccal  and  pharyngeal  cavities,  the  pitch 
of  which  depends  upon  the  pitch  of  the  voice,  just  as  the 
pitch  of  an  overtone  depends  upon  the  fundamental  tone. 

Consonants  are  sounds  not  accompanied  by  the  voice. 
They  are  classified  as : 

1.  Resonants;  ;//,  //,  ng\  produced  by  closing  the  mouth 
and  driving  the  air  through  the  nose. 

2.  Explosives;  b,  p,  d,  /,  g,  k\  produced  by  the  forma- 
tion of  an  obstruction  to  the  expired  air,  or  the  removal  of 
such  an  obstruction  (the  nasal  passage  being  closed). 

3.  Aspirates;  w,  /",  s,  /,  sh,  .z,  ,c//,  ///,  j,  ch\  produced 
by  driving  the  expired  air  through  a  constricted  portion  of 
the  mouth. 

4.  Vibratories ;  r\  produced  by  the  exhaled  air  throwing 
the  walls  of  a  constricted  portion  of  the  buccal  cavity  into 
vibration. 

According  to  the  position  of  the  obstruction  or  constric- 
tion in  the  buccal  cavity  we  can  distinguish  between  labials, 
dentals,  and  gutturals. 

The  sound  of  //  is  formed  when  the  exhaled  air  is  un- 
obstructedly  driven  through  the  mouth  while  the  nasal 
passage  is  closed. 


CHAPTER    XVI 

GENERAL   NERVE   PHYSIOLOGY 

1.     THE     CONSTRUCTION     AND     FUNCTION     OF     THE 
NERVE    ELEMENTS 

The  nervous  system  is  composed  of  nerve  units  called 
neurons.      The  neuron  is  made  up  of: 

(i)  A  nerve  cell,  and  (2)  its  processes,  which  ma}'  be 
divided  into : 

(a)  Protoplasmic  processes  or  dendrites,  which  are  short, 
much-branching  processes,  rapidly  decreasing  in  size. 

{b)  An  axis-cylinder  process  or  neurite,  which  differs  from 
the  dendrites  in  its  hyaline,  smooth  appearance.  Its  thick- 
ness is  uniform  throughout  its  course.  At  the  end  it  splits 
up  into  a  group  of  brushes,  the  so-called  end-tufts.  Many 
axis-cylinders  give  off  lateral  branches  (collaterals)  which 
also  end  in  tufts.  The  axis-cylinder,  the  most  important 
part  of  each  nerve  fibre,  is  sometimes  longitudinally  striated 
owing  to  the  fibrils  of  which  it  is  composed.  Between  the 
fibrils  is  found  the  neuroplasma,  a  finely  granular  substance. 

The  physiological  processes  in  this  nerve  unit  are  such 
that  when  the  cell  is  stimulated  either  automatically  (without 
any  outside  stimulation)  or  by  some  outside  stimulation, 
which  is  taken  up  by  the  protoplasmic  processes  and 
carried  to  the  cell.  The  stimulation  is  also  taken  up  by 
the  axis-cylinder  which  conducts  it  to  the  end-tufts.  Thence 
it  is  communicated  to  the  organ  with  which  the  end-tufts  are 
connected  (cells  of  other  nerve  elements,  muscle  fibres,  or 
gland  cells. 

The  protoplasmic   processes  earn-  the  stimulation  celluli- 

215 


216  HUMAN  PHYSIOLOGY 

petally,  i.e.  to  their  cells;  the  axis-cylinders  carry  it  cellu- 
lifugally,  or  from  their  cells.  Accordingly,  the  peripheral 
sensory  nerves  which  carry  the  stimuli  cellulipetally  must 
be  regarded  not  as  axis-cylinder  processes  but  as  elongated 
protoplasmic  processes. 

The  process  of  irritability  and  conductivity  of  the  indi- 
vidual neuron  is  the  elementary  physiological  process  which 
lies  at  the  basis  of  the  functions  of  the  nervous  system. 

The  transmission  of  the  stimulation  from  one  neuron  to  another 
is  perhaps  accomplished  by  delicate  nerve  fibrillar  which  connect 
the  end-tufts  of  one  neuron  with  the  protoplasmic  processes  of 
another  neuron.  But  it  is  difficult  to  demonstrate  such  fibrillse 
anatomically. 

Neuroglia  and  medullary  sheaths  appear  to  be  supporting  and 
protecting  organs  for  the  real  nerve-substance. 

General  nerve  physiology  is  divided  into  two  parts,  corre- 
sponding to  the  two  parts  of  the  neuron. 

1.  General  physiology  of  the  nerve  fibres, — including  the 
sensory  nerves  which  must  really  be  regarded  as  dendrites. 

2.  General  physiology  of  the  nerve  cells. 

•>.    GENERAL     PHYSIOLOGY    OF    THE    NERVE    FIBRES 

i .   The   irritability  and  conductivity  of   nerves. — The 

nerve  fibres  serve  to  carry  impulses  from  one  end-organ,  the 
receiving  organ  (sense  organ  or  nerve  cell),  to  the  other 
end-organ  (muscle,  gland  cell,  or  other  nerve  cell).  The 
stimulation  of  a  nerve  takes  place  normally  in  the  receiving 
organ,  but  can  also  be  applied  to  an)-  part  of  the  nerve  by 
artificial  stimulation. 

The  nature  of  the  impulse  and  of  the  conduction  of  the 
stimulation  is  not  known.  The  only  token  of  the  impulse 
which  has  been  observed  is  an  electrical  phenomenon.  An 
active  part  of  a  nerve  is  negative  to  the  resting  part.  The 
significance  of  this  phenomenon  is  not  known. 

In  Fig.  17  let  AB  be  a  nerve;  at  a  and  b  place  the  electrodes 
of  a  galvanometer  (/.),  and  stimulate  the  nerve  at  Cby  means  of 
an    induction     current.       Shortly    after    stimulation    the    impulse 


GENERAL   NERVE   PHYSIOLOGY  217 

reaches  a,  and  an  electric  current  passes  from  b  to  a  through  L. 
When  the  impulse  has  passed  a  and  is  carried  to  b,  a  current  passes 
from  a  to  b  through  L.  These  currents  are  called  action  currents. 
Their  rapidity  is  so  great  and  they  follow  each  other  so  closely  that 
they  cannot  be  demonstrated  by  an  ordinary  galvanometer.  They 
can  be  demonstrated  by  a  very  sensitive  electrometer  (capillary 
electrometer)  or  by  a  special  apparatus  in  which  the  action  upon 
a  magnetic  needle  is  intensified  by  a  series  of  action  currents 
moving  in  the   same  direction   and   rapidly  following  each   other 

C  h 


Fig.   17. 

through     the     galvanometer     (Bernstein's     repeating     differential 
rheotome). 

Cut  a  nerve  across,  place  one  electrode  of  the  galvanometer  on 
the  transverse  section  and  the  other  on  the  longitudinal  surface. 
A  current  will  pass  through  the  galvanometer  from  the  longitudinal 
to  the  transverse  section  (current  of  rest).  At  the  cut  surface  the 
nerve  immediately  begins  to  die,  and  this  is  accompanied  by 
processes  which  make  that  part  of  the  nerve  negatively  electrical 
to  the  sound  part.  If  in  such  a  case  a  certain  point  in  the  longi- 
tudinal surface  be  stimulated,  the  intensity  of  the  current  of  rest 
is  decreased,  that  is,  it  undergoes  a  negative  variation. 

Aside  from  these  electrical  changes,  the  nerve  impulse 
can  only  be  detected  by  the  effects  which  it  has  upon  the 
end-organ  (muscular  contraction  in  the  motor  nerves,  sensa- 
tion in  the  sensory  nerves). 

2.   Laws  of  conductivity  of  nerves. 

(a)  Isolated  conduction. — In  a  nerve  trunk  composed  of 
many  fibres  the  impulse  does  not  pass  from  one  fibre  to 
another. 

{b)  Double  conduction. — A  nerve  artificially  stimulated  at 
a  certain  point  conducts  the  impulse  not  only  in  the  direc- 
tion in  which  it  is  conducted  under  physiological  conditions, 
but  also  in  the  opposite  direction. 

The  nerve  supplying  the  gracilis  muscle  of  the  frog  divides  into 
two  branches,  of  which  the  one  supplies  the  upper  and  the  other 
the  lower  half  of  the  muscle.      At  the  forking  of  the  nerve,  the 


2i8  HUMAN  PHYSIOLOGY 

axis-cylinders  divide,  so  that  each  axis-cylinder  gives  a  branch  to 
the  lower  and  to  the  upper  half  of  the  muscle.  If  the  muscle  is 
cut  transversely  without  injury  to  the  fork  of  the  nerve  and  one  of 
the  branches  of  the  fork  be  stimulated,  both  halves  of  the  muscle 
contract.  Hence  the  impulse  of  the  stimulated  nerve  passes  not 
only  in  the  centrifugal  but  also  in  the  centripetal  direction,  and 
then,  in  the  other  branch,  passes  in  the  centrifugal  direction". 

The  electrical  phenomenon  also  spreads  in  both  directions  from 
the  place  artificially  stimulated. 

(c)  Velocity  of  the  impulse. — The  velocity  of  the  nerve 
impulse  in  an  excised  frog  nerve,  at  room  temperature,  is 
27  metres  per  second.  In  man  it  lias  been  variously  stated 
(between  30  and  60  m  per  second). 

The  velocity  of  the  impulse  is  measured  as  follows  :  Take  a  frog 
muscle-nerve  preparation  and  stimulate  the  nerve  in  two  places, 
one  at  a  place  as  near  to,  the  other  as  far  removed  from,  the  mus- 
cle as  possible.  Determine  the  difference  in  latent  period  |  the 
lapse  of  time  between  the  stimulation  and  the  beginning  of  ion- 
traction).  This  can  be  done  best  by  graphically  recording  the 
contraction.  The  latent  period  following  the  stimulation  of  the 
point  far  removed  from  the  muscle  is  greater  than  that  following 
the  stimulation  of  the  point  near  the  muscle.  The  difference 
between  the  latent  periods  is  the  time  it  takes  for  the  impulse  to 
travel  the  distance  between  the  two  points  stimulated.  From  this 
it  can  be  calculated  how  great  a  distance  the  impulse  travels  in  one 
second. 

Experiments  based  on  the  same  principle  have  been  made  upon 
human  beings,  but  the  results  are  not  constant. 

3.  Stimulation  and  changes  in  irritability. — The  stimu- 
lating influences  in  many  cases  also  produce  changes  in 
irritability  and  conductivity.  Hence  we  may  properly  con- 
sider these  actions  collectively. 

(a)  Mechanical  influences. — Hitting,  pulling,  squeezing, 
cutting,  and  drying  stimulate  the  nerve,  but  also  destroy  its 
irritability  and  conductivity. 

(l?)  Thermal  influences. — Temperatures  above  45 °  C.  and 
below  freezing-point  destroy  irritability  and  conductivity. 
Within  the  limits  of  temperatures  which  are  not  injurious, 
irritability  and  conductivity  increase  with  the  temperature. 
Sudden  great  changes  in  temperature  stimulate,  e.g.  touch- 
ing a  nerve  with  a  red-hot  needle. 


GENERAL   NERVE  PHYSIOLOGY  219 

(c)  Chemical  influences.- — These  maybe  classified  as: 

1 .  Those  which  destroy  irritability  and  conductivity  with- 
out previously  stimulating,  e.g.  acids,  ammonia. 

2.  Those  which  first  stimulate  and  then  paralyze,  e.g. 
concentrated  salt  solution,  glycerin. 

If  a  part  of  a  motor  nerve  is  acted  upon  by  carbon 
dioxide,  that  part  of  the  nerve  loses  its  irritability  for  elec- 
trical stimulations,  but  does  not  lose  its  conductivity;  for  if 
the  stimulation  is  applied  above  the  place  acted  upon  by  the 
carbon  dioxide,  the  impulse  is  still  carried  to  the  muscle. 
Hence  irritability  and  conductivity  are  to  a  certain  extent 
independent  of  each  other. 

(d)  Electrical  influences.  —  A  constant  current  passed 
longitudinally  through  a  stretch  of  nerve  of  sufficient  length 
causes : 

1.  When  made,  stimulation  and  increased  irritability  at 
the  kathode  (place  of  exit  of  current) ;  decreased  irritability 
and  conduction  at  the  anode  (place  of  entrance). 

2.  When  broken,  decreased  irritability  and  conduction, 
for  a  short  time,  at  the  kathode;  stimulation  and  also  in- 
creased irritability  at  the  anode,  lasting  for  a  short  time. 
Stimulation  by  the  electrical  current  which,  in  a  motor 
nerve,  is  manifested  by  the  contraction  of  the  muscle,  as  a 
rule  takes  place  only  at  the  moment  of  the  making  and  the 
"breaking  of  the  current  (make  and  break  contraction) ;  more 
rarely  it  stimulates  for  some  time  during  its  passage  through 
the  nerve  (make-tetanus)  and  for  some  time  after  the  break- 
ing (break-tetanus).  Hence  the  extent  of  stimulation  of  a 
nerve  depends  chiefly  on  the  changes  in  the  strength  of  the 
current,  not  upon  its  absolute  intensity.  Changes  in  the 
strength  of  the  current  are  the  more  effective  the  more 
rapidly  they  take  place.  For  this  reason,  when  the  current 
is  not  suddenly  made  or  broken  but  is  made  and  broken 
gradually,  no  contraction  results.  The  make  contraction  is 
■stronger  than  the  break  contraction,  so  that  a  feeble  but  still 
active  current  produces  a  contraction  only  at  the  make. 


2  20  HUMAN  PHYSIOLOGY 

The  electric  current  does  not  stimulate  if  it  passes  trans- 
versely through  the  nerve. 

In  Fig.  1 8  let  A'be  the  nerve  of  a  muscle-nerve  preparation,  and 
let    the   current  enter  at  +  and  leave  at  — .     Determine  the  latent 
■y-  period   for  the    make  and   break   contraction 

(in  a  similar  manner  as  in  determining  the 
velocity  of  the  impulse,  page  219).  It  will 
be  found  that  the  latent  period  of  the  make  is 
greater  than  that  of  the  break  contraction. 
If  now  the  current  is  passed  through  the  nerve 
l'|,;-  l8-  in  the  opposite  direction,  it  will  be  found  that 

the  latent  period  of  the  make  is  smaller  than  that  of  the  break 
contraction.  The  difference  in  these  latent  periods  corresponds 
to  the  time  taken  by  the  impulse  to  travel  through  the  piece  of 
nerve  between  the  two  electrodes.  This  proves  that  the  stimula- 
tion of  the  making  of  the  current  takes  place  at  the  kathode,  while 
that  of  the  breaking  occurs  at  the  anode. 

The  changes  in  the  irritability  which  the  current  produces  at 
the  electrode  are  investigated  as  follows: 

The  nerve  is  stimulated  near  either  electrode  of  the  constant 
current  by  a  stimulus  of  constant  strength,  first  before  the  con- 
stant current  is  passed  through  the  nerve,  and  then  while  the 
constant  current  is  passing  through  the  nerve.  Observe  whether 
the  contraction  in  the  second  case  is  larger  or  smaller  than  that  in 
the  first. 

The  irritability  is  changed  during  the  entire  passage  of  the 
current.  This  condition  of  changed  irritability  produced  by 
the  current  is  called  electrotonus ;  the  condition  of  increased 
irritability  at  the  kathode  is  called  katelectrotonus ,  the  con- 
dition of  decreased  irritability  at  the  anode. is  called  anelec- 
trotonus.  We  may  express  these  observations  in  the  law : 
The  appearance  of  katelectrotonus  and  the  disappearance  of 
an  electrotonus  stimulate. 

The  decreased  conductivity  occurring  at  the  anode  during 
the  making  and,  for  a  short  period,  at  the  kathode  during 
breaking,  is  so  great,  when  strong  currents  are  used,  that  the 
nerve  at  these  places  loses  its  conductivity  altogether.  If  a 
part  of  a  nerve  which  has  lost  its  conductivity  is  situated 
between  the  place  stimulated  and  the  cncl-organ  (muscle), 
the  stimulation  has  no  result.  This  occurs  in  the  following 
cases: 


GENERAL    NERVE   PHYSIOLOGY  221 

(1)  During  making",  when  the  anode  lies  between  the 
end-organ  and  the  kathode. 

(2)  During  breaking,  when  the  kathode  lies  between  the 
end-organ  and  the  anode. 

Lazv  of  contraction. — From  the  above-mentioned  facts  the 
following  relations  between  the  stimulation  of  a  muscle  and 
the  strength  of  a  current  and  its  direction  through  the  motor 
nerve  can  be  formulated : 


Strength  of  Current. 

Ascending  Current. 

Descending  Current. 

Weak 

Make 
Break- 

Contraction 
Rest 

Contraction 
Rest 

Moderate 

Make 
Break 

Contraction 

Rest 

Contraction 

Contraction 

Strong 

Make 
Break 

Contraction 
Rest 

The  current  is  ascending  when  it  passes  through  the  nerve  from 
the  muscle  to  the  centre;  it  is  descending  when  it  passes  from  the 
centre  to  the  muscle. 

The  law  of  contraction  may  be  explained  thus:  In  a  weak  cur- 
rent only  a  stronger  stimulus  is  active,  i.e.  the  appearance  of 
katelectrotonus  stimulates;  not  so  the  disappearance  of  anelectro- 
tonus,  hence  a  contraction  occurs  only  by  the  making.  In  a 
moderate  current  both  the  appearance  of  katelectrotonus  and  the 
disappearance  of  anelectrotonus  stimulate,  hence  both  a  make  and 
a  break  contraction  result. 

In  a  strong  ascending  current  the  make  contraction  fails, 
because  the  stimulation  at  the  kathode  cannot  pass  through  that 
part  of  the  nerve  where  the  conductivity  has  been  decreased  at  the 
anode.  In  a  strong  descending  current  the  break  contraction 
fails,  because  the  stimulation  at  the  anode  cannot  pass  through 
the  non-conducting  part  of  the  nerve  at  the  kathode. 

A  current  passing  through  a  stretch  of  medullated  nerve  spreads 
throughout  the  whole  nerve;  also  to  that  part  of  the  nerve  beyond 
the  electrodes.  If  the  two  electrodes  of  a  galvanometer  are  placed 
upon  the  nerve  exterior  to  the  part  stimulated,  a  current  passes 
through  the  galvanometer  because  of  this  spreading.  This 
phenomenon  is  of  physiological  interest,  for  this  spreading  is  due 
to  a  peculiar  polarization  of  living  nerve  fibres.  This  spreading 
■of  the  current  cannot   be  demonstrated  in  a  dead  nerve.      The 


22  2  HUMAN  PHYSIOLOGY 

whole  phenomenon  has  been  called  physical  electrotonus  in 
distinction  from  physiological  electrotonus  (change  of  irritability). 
The  electrical  resistance  of  the  nerve  in  the  direction  of  the 
fibre  is  2^  million,  in  the  transverse  direction  i  2}T  million,  times 
as  great  as  that  of  mercury. 

Induced  currents  stimulate  at  the  kathode  only,  hence  act 
as  weak  currents  in  respect  to  the  law  of  contraction. 

The  uninjured  motor  nerves  in  the  human  body  seem  to 
follow  other  laws  of  contraction  than  the  excised  nerves  of 
a  nerve-muscle  preparation.  When  one  electrode  is  placed 
on  the  skin  above  a  nerve  to  be  investigated  and  the  other 
on  some  indifferent  part  of  the  body  (back,  neck)  remote 
from  the  first  electrode,  a  make  contraction  follows  the 
feeblest  but  yet  effective  current  when  the  electrode  placed 
on  the  nerve  is  the  kathode  (kathode-make  contraction). 
A  little  stronger  current  produces  anode-make  and  anode- 
break  contraction  (when  the  electrode  on  the  nerve  is  the 
anode),  and,  in  a  very  strong  current,  also  the  kathode- 
break  contraction.  This  apparent  deviation  from  the  law 
of  contraction  is  due  to  the  nature  of  the  spreading  of  the 
current  in  the  human  body.  The  nerve,  in  this  case,  is 
traversed  by  the  branching  currents  in  diagonal  and  trans- 
verse directions,  not  merely  longitudinally  as  in  the  excised 
nerve. 

(e)  Irritability  and  conductivity  depend  also  upon  normal 
vital  conditions.  Not  only  do  excised  nerves  gradually 
lose  their  irritability  and  conductivity,  but  also  nerves  which 
have  lost  (by  cutting,  disease)  their  normal  connection  with 
the  nerve  cells.  A  nerve  thus  severed  dies,  the  axis-cylinder 
and  the  medullary  sheath  disappearing  and  connective  tissue 
being  deposited.  Sometimes  regeneration  of  the  nerve  trunk 
still  connected  with  the  cell  takes  place. 

A  change  in  the  irritability  of  the  nerve  by  fatigue  has 
not  yet  been  definitely  proven. 

Nothing  is  known  concerning  the  chemical  composition  of  the 
real  nerve-substance.  No  processes  of  metabolism  have  ever  been 
demonstrated  in  the  stimulated  or  unstimulated  nerve.  The 
metabolism   is,  at  any  rate,  even  in  stimulated  nerves,  very  slight. 


GENERAL    NERVE  PHYSIOLOGY  223 

for  nerves  do  not  appear  susceptible  to  fatigue,  and  the  supply  of 
blood  to  them  is  small. 

Neurokeratin  is  found  in  the  neuroglia;  fat,  cholcsterin,  lecithin, 
and  protagon,  in  the  medullary  sheath. 

4.  The  effect  of  the  conduction  of  the  impulse. — The 
nature  of  the  result  of  the  conduction  of  the  impulse  to  the 
end-organ  does  not  depend  upon  the  nature  of'the  stimula- 
tion, but  upon  the  nature  of  the  end-organ.  For  example, 
each  effective  stimulation  of  a  motor  nerve  is  followed  only 
by  a  muscular  contraction,  of  a  secretory  nerve  by  secretion, 
of  a  sensory  nerve  only  by  sensation.  In  the  last  case  only 
that  kind  of  sensation  is  produced  which  is  specific  for  the 
sense  cell  of  the  organ  acted  upon. 

The  nerve  fibres  may  be  classified  as  to  the  direction  in 
which  they  normally  carry  the  impulse  as: 

1.  Centrifugal  ( motor,  secretory;,  conducting  the  impulse 
from  the  nerve  cell  to  the  peripheral  organ. 

2.  Centripetal  (sensory,  nerves  acting  reflexly),  conduct- 
ing from  a  sense  organ  to  a  nerve  cell. 

3.  Intercentral  conduction  from  one  nerve  cell  to  another. 

Besides  conducting  the  impulses  the  nerve  fibres  have  an  influ- 
ence on  the  nutrition  of  the  organs  which  they  innervate.  After  the 
nerves  have  been  cut,  the  organs  which  they  supply  undergo  dis- 
turbances of  nutrition,  e.g.  the  dying  of  a  muscle  after  section  of 
its  nerves. 

3.   GENERAL    PHYSIOLOGY    OF    THE    NERVE    CELLS 

All  the  functions  of  the  nervous  system  which  we  cannot 
explain  from  the  known  functions  of  the  nerve  fibres  we 
ascribe  to  the  nerve  cell,  for  no  other  nerve  elements  are 
known  to  which  they  can  be  ascribed.  These  functions  do 
not  belong  to  the  whole  nerve  cell,  but  to  parts  of  the  pro- 
toplasm.    The  nucleus  has  probably  only  a  trophic  function. 

The  trophic  action  of  nerve  cells  is  illustrated  by  the  fact  that 
nerve  fibres  separated  from  the  nerve  cells  degenerate.  In  many 
cases  this  is  also  true  for  end-organs  (muscles)  supplied  by  these 

nerve  fibres. 


224  HUMAN  PHYSIOLOGY 

The  nerve  cells  are  irritable.  Their  physiological  stimu- 
lation is  of  two  kinds: 

i .  The  stimulation  originates  by  processes  in  the  cells 
themselves — automatic  activity.  The  automaticity  is  either 
tonic,  when  the  impulse  travels  continuously  through  the 
nerve  fibre  connected  with  the  cell,  or  rhythmic,  when  the 
impulse  proceeds  periodically  down  the  nerve  fibre.  For 
example,  lack  of  oxygen  and  accumulation  of  carbon 
dioxide  stimulate  the  cells  of  the  respirator}'  centre;  they 
are  conditions  which  the  cell  itself  produces  by  its  meta- 
bolism. The  automaticity  of  the  respirator}-  centre  is 
rhythmic.  The  vaso-motor  centre  is  also  stimulated  by 
lack  of  oxygen  and  accumulation  of  carbon  dioxide;  its 
automaticity  is  tonic. 

2.  The  stimulation  is  carried  to  the  cell  by  a  nerve  fibre. 
As  the  stimulation  can  be  conducted  from  this  cell  to  its 
axis-cylinder,  there  results  the  conduction  of  impulses  from 
one  nerve  fibre  to  another  through  the  nerve  cell.  The 
conduction  of  the  impulse  through  the  cell  differs  from  that 
through  the  fibres  in  the  following  points: 

(a)  The  cell  is  able,  independently,  to  modify  the  impulse 
either 

(a)  In  intensity:  it  can  increase  or  decrease  the  strength 
of  the  impulse ; 

(/J)    In  frequency  of  the  impulse. 

For  example,  the  impulses  which  in  the  radiated  reflexes 
(see  page  231)  affect  the  muscles  are  not  proportional  to 
the  strength  and  frequency  of  the  sensor}-  stimulation  which 
calls  forth  the  reflex. 

(/;)  The  conduction  is  not  double,  but  passes  in  one 
direction  only.  In  the  spinal  cord,  for  example,  the  impulse 
passes,  in  reflex  action,  from  the  sensory  nerve  through  the 
cell  to  the  motor  fibres,  but  newer  in  the  reverse  direction. 
The  electrical  phenomena  characteristic  of  the  impulse  can- 
not be  called  forth  in  the  sensor}-  nerve  by  the  stimulation 
of  the  motor  roots. 


GENERAL   NERVE   PHYSIOLOGY  225 

(c)  The  velocity  of  the  conduction  of  the  impulse  through 
the  cells  is  much  less  than  that  through  the  fibres. 

From  a  physiological  standpoint,  the  individual  processes 
of  conduction  through  the  cells  differ  from  each  other  only 
in  the  number  of  the  impulses  passing  through  the  neurons, 
and  in  the  modification  of  the  impulse  in  the  cells.  From  a 
psychical  standpoint  we  may  classify  the  processes  of  con- 
duction through  nerve  cells  into : 

1.  Conduction  of  impulses  through  the  cells  not  accom- 
panied by  consciousness.  This  includes  the  reflexes,  i.e. 
the  transferring  of  an  impulse  from  a  centripetal  fibre  through 
a  centre  to  a  centrifugal  fibre  Avithout  resulting  in  conscious- 
ness, which  may  indeed  occur  against  the  will. 

2.  Psycho-physical  processes,  which  are  accompanied  by 
consciousness.  The  transferring  of  the  impulse  from  the 
sensory  nerve  fibre  through  the  central  nervous  system  to 
the  motor  nerve,  which  occurs  voluntarily,  is  called  "volun- 
tary reaction,"  in  distinction  from  reflex  action. 

The  chemical  processes  which  take  place  in  the  resting  and  the 
active  nerve  cells  are  not  known.  That  they  are  intense  is  apparent 
from  the  fact  that  even  temporary  cessation  of  the  blood  supply  soon 
causes  injury.  Death  of  the  nervous  system  through  asphyxia 
occurs  in  warm-blooded  animals  in  a  few  minutes. 


CHAPTER    XVII 

THE    SPINAL   CORD 

Anatomy. — The  cylindrical  spinal  cord  is  composed  of  a  column 
of  gray  matter  surrounded  by  a  layer  of  white  matter.  In  the  cross- 
section  the  gray  substance  has  the  form  of  an  H. 

Each  half  of  the  white  substance  is  divided  by  the  gray  substance 
into  three  columns,  the  anterior,  lateral,  and  posterior.  From 
between  the  anterior  and  the  lateral  columns  the  anterior  roots  of 
the  peripheral  nerves  proceed,  and  from  between  the  lateral  and 
the  posterior  columns,  the  posterior  roots.  In  each  of  the  three 
columns  the  following  separate  bundles  may  be  discriminated  (com- 
pare Fig.   19)  : 

1.  In  the  anterior  column  : 

(V)    Direct  pyramidal  tract. 
(b)   Anterior  ground  bundle. 

2.  In  the  lateral  column  : 

(  c  )   Crossed  pyramidal  tract. 

((/)    Direct   cerebellar  tract    whose  anterior  part   is   called 

(lower's  column. 
(e)   Lateral  bundles. 

3.  In  the  posterior  column  : 

(/")    Coil's  column. 
(g)   Burdach's  column. 

The  white  matter  contains  medullated  nerve  fibres  ;  the  gray 
matter  is  chiefly  composed  of  nerve  cells. 

The  functions  of  the  spinal  cord  consist  in  conducting  im- 
pulses through  fibres  and  cells.  They  may  be  divided  into 
three  main  groups : 

(1)  The  conduction  of  the  impulses  in  the  motor  tracts 
from  the  brain  through  the  cord  to  the  peripheral  nerves. 

(2)  The  conduction  of  impulses  from  the  peripheral 
sensory  nerves  through  the  cord  to  the  brain. 

226 


THE  SPINAL    CORD 


227 


(3)  Conduction  of  impulses  from  the  peripheral  centripetal 
nerves     through     the     cells  of    the 
gray    matter    of    the    cord    to    the 
peripheral  motor  nerves — reflexes. 

1.    THE    MOTOR    TRACTS 

These  are  formed  from  fibres  of 
hot!  1  pyramidal  columns,  the  cells  of 
the  anterior  horns  and  the  anterior 
roots. 

The  pyramidal  column  descend- 
ing from  the  brain  gives  off,  at  vari- 
ous heights,  fibres  into  the  gray 
substance,  hence  the  cross-section 
of  this  column  decreases  as  it  pro- 
ceeds downward.  The  end-tufts  of 
the  pyramid  fibres  come  into  con- 
tact with  the  cells  of  the  anterior 
horns,  those  of  the  crossed  pyram- 
idal tract  are  in  contact  with  cells 
on  the  same  side,  while  those  of  the 
direct  pyramidal  tract  are  in  contact 
with  cells  on  the  opposite  side. 
The  fibres  of  the  direct  pyramidal 
tract    cross    in    the    anterior    white 

commissure  just  before  their  ending1  ^  ~ 

J  *=>   Fig.    19. — Cross-section    of 

at  the  cells.  the  Spinal  Cord  at  Va- 

-ri  •  t     1  j    -  ■  ,  rious      Heights,     demon- 

The  axis-cylinders  proceed  into      STRATINGTHE  columns  of 

the  anterior  roots  from  the  cells  of      the  White  Matter. 
,,  .  (After  Fleclisisr.) 

the  anterior  horn.  T        .    ,         •    , 

1,  at  sixth  cervical  nerve;  II, 

Pathological  evidence  shows  that    at    third  dorsal    nerve;    III,   at 

.1  -I       ■      ,     j  -i      j  sixth     dorsal      nerve:     IV,     at 

the  paths  just  described  are  motor.   twelfth   dorsal    nen/e.    ^    at 
There   are    diseases    in    which    the  fourth  lumbar  nerve,  pv,  direct 

,  .  .      pyramidal     tract ;     ps,     crossed 

motor  nerves    only  are    paralyzed,   pyi-amidal  tract;  ks,  direct  cere- 
and  in  these  cases    the    pyramidal  bellar  tract;  ,§-,  Goll's  column, 
columns    and    the     cells     of    the     anterior    horns    undergo 


228  HUMAN  PHYSIOLOGY 

anatomical  changes  (disappearance  of  the  nerve  tissue  and 
the  replacement  of  it  by  connective  tissue).  The  results 
of  anatomic  investigations  of  the  course  of  these  fibres 
agree  with  the  pathological  evidences. 

After  transverse  severing  of  the  cord  (by  injury  or  disease; 
a  secondary  degeneration  of  the  pyramidal  column  below 
the  injury  takes  place.  Since  a  nerve  fibre,  severed  from 
its  nerve  cell,  degenerates  (see  page  223),  this  leads  to  the 
conclusion  that  the  cells  of  the  pyramid  fibres  lie  in  the  brain. 

Of  the  nerves  derived  from  the  centrifugal  tracts  of  the  cord  must 
be  mentioned  the  nerves  for  respiration  and  perspiration  and  the 
vaso-motor  nerves  (see  pages  75,  83  and  109).  A  few  fibres 
(vasodilators  and  motor  fibres  for  the  intestine)  are  supposed  to 
leave  the  cord  by  posterior  roots. 

2.    THE    SENSORY   TRACTS 

These  are  paths  which,  emanating  from  the  fibres  of  the 
posterior  roots,  pass,  either  directly  or  by  the  interposition  of 
cells  throughout  Goll's  column  through  the  direct  cerebellar 
tract  and,  as  scattered  fibres,  through  the  lateral  bundle. 

The  peripheral  sensory  fibres  end  directly  in  the  cells  of 
the  spinal  ganglia.  They  are  really  elongated  dendrites  of 
these  cells  (see  page  215).  From  these  cells  the  axis- 
cylinders  proceed  through  the  posterior  roots  into  the  spinal 
cord  and  there  separate  into  two  large  groups: 

1.  Fibres  which  cross  the  Burdach  column  diagonally, 
reach  Goll's  column  and  through  this  proceed  upward  to  the 
brain. 

2.  Fibres  the  end-tufts  of  which  come  into  contact  with 
the  cells  of  the  gray  substance.  The  neurites  of  these  cells 
pass 

(a)  To  the  direct  cerebellar  tract  on  the  same  side,  and  in 
this  tract  proceed  upward  to  the  brain.  The  cells  of  these 
neurites  lie  in  the  columns  of  Clark,  which  are  masses  of 
cells  on  the  median  side  of  the  basis  of  the  posterior  horns. 

(/>)  Through  the  gray  or  white  commissure  to  the  other 
side,  and  pass  upward  as  scattered  fibres  in  the  lateral 
bundles,  or  perhaps  also  in  Gower's  column. 


THE  SPIXAL    CORD  229 

Tabes  dorsalis  is  a  disease  of  the  spinal  cord  in  which  the 
sensory  nerves  only  are  paralyzed,  and  the  posterior  roots 
and  Goll's  columns  are  degenerated.  Hence  Goll's  columns 
are  sensory  tracts. 

After  transverse  section  of  the  spinal  cord,  secondary 
degeneration  of'the  fibres  of  Goll's  columns  and  the  direct 
cerebellar  tract  above  the  section  takes  place ;  hence  the 
cells  of  these  fibres  lie  below  the  section. 

Half-section  of  the  cord. — If,  by  injury,  one  lateral  half 
of  the  cord  has  been  cut  through,  motor  paralysis  below 
and  on  t'he  same  side  of  the  injury  occurs,  while  on  the 
opposite  side  there  is  chiefly  loss  of  sensation.  The  injured 
motor  columns  lie,  therefore,  mainly  on  the  same  side  as 
the  corresponding  peripheral  motor  nerves.  The  injured 
sensory  columns  lie,  however,  chief!}-  on  the  side  opposite 
to  the  corresponding  peripheral  sensor}'  nerves;  this  depends 
upon  the  above-mentioned  crossing  (2b)  of  the  sensor}-  fibres 
in  the  gray  matter. 

This  brief  review  of  the  sensory  tracts  relates,  in  general,  the 
facts  as  they  are  known  at  present  ;  but  the  conditions,  in  detail, 
are  much  more  complicated,  for  the  long  fibres  in  the  spinal  cord 
give  off  branches  downward  and  laterally,  ending  in  the  gray  matter. 
For  example,  each  of  the  fibres  of  the  posterior  roots  which  enters 
the  posterior  columns  divides  into  two  long  branches,  the  heavier 
one  proceeding  upward  and  finally,  with  Golfs  column,  reaches  the 
medulla  oblongata  ;  the  other  going  downward  and,  after  a  short 
course,  ending  in  the  gray  matter.  Both  these  branches  give  off 
collaterals  which  also  end  in  the  gray  matter.  The  cells  in  the  gray 
substance  to  which  the  ends  of  the  descending  and  collateral 
branches  go  also  give  off  neurites  which,  under  the  giving  off  of 
collaterals,  form  long  tracts  or,  after  a  short  course,  end  in  the  grav 
substance.  Hence  there  is  no  such  sharp  distinction  between  the 
long  sensory  tracts  and  the  reflex  tracts  to  be  described  presently, 
as  would  appear  from  the  above  description. 

3.   REFLEXES  OF  THE   SPIXAL  CORD 

Nature  of  the  reflex. — The  reflex  is  the  transferring  of  a 
stimulation  from  a  centripetal  to  a  centrifugal  nerve  through 
the  centre.      This  occurs  involuntarilv.      According  to  the 


230 


HUM AN  PHYSIOLOGY 


effect  of  the  reflex  in  the  end-organ  of  the  centrifugal  nerve, 
we  distinguish  between  reflex  movement,  reflex  secretion, 
and  reflex  inhibition.  The  reflexes  of  the  spinal  cord  are 
chiefly  reflex  movements. 

The  reflex  tracts. — The  connections  of  centripetal  nerves 
with  motor  nerves  which  are  necessary  for  the  production  of 
reflex  movements  may  be  : 

(i)  Direct.  The  end-tufts  of  the  centripetal  fibres  and 
the  collaterals  are  in  direct  contact  with  the  motor  cells. 

(2)  Indirect.  Between  the  centripetal  and  the  motor 
neurons  other  neurons  intervene. 

The  direet  and  indirect  tracts  are  illustrated  in  Fig.  20.  In  this 
figure  a  represents  the  motor  cells  and  roots  ;  b  is  a  spinal  ganglion 
with  its  root.  The  sensory  collateral  r  joins  the  motor  cells  directly, 
forming  a  direct  reflex  tract.     The  sensory  collateral  c  first  joins  the 

cell  d  whose  axis-cylinders  make 
connections  with  the  motor  cells 
through  the  collaterals  e,  e,  e. 
This  constitutes  an  indirect  re- 
flex tract. 

The  direct  reflex  tract  dif- 
fers, therefore,    from    the    in- 
L-^^  ^      )  \'A  direct  in   that  but  two  kinds 

of  cells  arc  intercalated  in  its 
course,  namely,  the  cells  of 
the  spinal  ganglion  and  the 
^  motor  cells  of  the  anterior 
horn.  In  the  indirect  tract 
one  or  more  cells  are  placed 
between  these  two  kinds  of 
cells. 

It     is     apparent    that    the 

union      of     centripetal     with 

motor  nerves  may  take  place 

in   a   great   man}'  ways,  as   is   also  required  by  the  manifold 

spreading  of  the  reflex.     The  fibres  of  these  reflex  tracts,  by 

which  various  heights  of  the  gray  matter  are  connected  with 


THE  SPINAL    CORD  231 

each  other,,  run  chiefly  in  the  anterior  ground   and    lateral 
bundles  and  the  columns  of  Burdach. 

Classification  of  the  reflexes. — The  reflex  movements  executed 
by  the  aid  of  the  spinal  cord  can  most  readily  be  studied  in  cold- 
and  warm-blooded  animals  in  winch  the  action  of  the  brain  is  ex- 
cluded by  a  section  between  the  brain  and  spinal  cord. 

According  to  the  degree  of  spreading  of  the  reflex  move- 
ment we  may  discriminate : 

1.  Simple  or  partial  reflexes.  The  stimulation  of  a 
sensory  spot  is  followed  by  the  movement  of  only  one 
muscle  or  of  a  limited  group  of  muscles.  Example:  knee- 
jerk.  If  the  sensory  nerve  of  the  ligamentum  patellae  is 
stimulated  by  hitting  the  ligament,  the  quadriceps  femoris 
muscle  contracts  by  reflex  action  and  the  lower  part  of  the 
leg  is  thrown  forward. 

2.  Radiated  reflexes.  Stimulation  of  a  sensory  area 
results  in  the  contraction  of  large  groups  of  muscles  or  of  all 
the  muscles  of  the  body.      We  may  classify  them  as: 

(a)  Orderly  radiated  reflexes.  The  stimulation  is  fol- 
lowed by  a  movement  with  the  purpose  of  removing  the 
stimulus  or  fleeing  from  it.  If,  for  example,  the  leg  of  a 
decapitated  frog  is  moistened  with  a  drop  of  acid,  the  frog 
wipes  off  the  acid;  if  the  foot  is  pinched  or  pricked,  it  tries 
to  flee.  These  reflectory  defensive  movements  can  also  be 
observed  in  man  during  sleep. 

The  movements  appear  to  us  as  voluntary  movements, 
but  whether  they  are  accompanied  by  consciousness  in  the 
cells  of  the  spinal  cord  cannot  be  determined,  for  we  have 
no  knowledge  of  any  subjective  perception  in  the  cells.  It 
is  of  interest  to  note  that  the  cells  of  the  spinal  cord  are  able 
independently  to  change  the  afferent  impulses  into  a  pur- 
poselike muscular  activity  and  are,  therefore,  from  a  physio- 
logical standpoint,  not  different  from  the  cells  of  the  cerebral 
hemispheres  in  which  the  psycho-physical  processes  take 
place. 

(£)   Disorderly  radiated  reflexes  or  convulsive  reflexes. 


232  HUMAN  PHYSIOLOGY 

By  stimulation  of  a  sensor}-  spot,  uncoordinated  contrac- 
tions of  larger  groups  of  muscles,  even  of  all  the  muscles, 
may  take  place.  Examples:  convulsions  during  teething; 
convulsions  in  strychnine  poisoning.  In  adults  convulsive 
reflexes  seldom  occur,  and  only  after  very  strong  stimulation 
fill  intense  neuralgia). 

As  a  stimulation  of  any  sensory  fibre  may  call  forth  con- 
vulsive reflexes,  connections  between  all  the  sensor}'  fibres 
and  all  the  motor  fibres  must  exist.  These  connections  are 
normally  irritable,  but  not  all  to  the  same  extent,  so  that 
the  impulse  radiates  over  certain  tracts  and  thus  causes 
orderly  reflexes. 

Reflex  time  is  the  time  elapsing  between  the  entrance  of 
the  impulse  into  the  spinal  cord  and  the  passing  out  through 
the  motor  paths.  It  is  determined  by  measuring  the  time 
elapsing  between  the  beginning  of  the  stimulation  and  the 
beginning  of  the  contraction,  and  subtracting  from  it  the 
latent  period  of  the  muscle  and  the  time  taken  by  the  stimu- 
lation to  travel  through  the  sensory  and  motor  nerves.  The 
reflex  time  is  0.008-0.015  second. 

Influences  affecting  the  reflexes. — Reflex  action  depends 
upon 

(a1)  The  strength  of  the  stimulus. — To  call  forth  a  reflex 
the  stimulus  must  be  of  a  certain  strength.  Very  strong 
stimulations,  however,  can  inhibit  the  reflexes.  The  reflex 
time  is,  within  certain  limits,  the  shorter  the  stronger  the 
sensor}'  stimulation. 

{JS)  The  number  and  sequence  of  the  stimuli. — A  greater 
number  of  successive  and  weaker  currents  can  more  readily 
call  forth  reflexes  than  a  single  strong  induction  current. 

{y)  The  place  of  stimulation.  —  The  reflexes  are  more 
easily  called  forth  by  stimulation  of  the  sensor}-  apparatus 
in  the  skin  than  by  direct  stimulation  of  the  nerve  trunk. 

Reflex  irritability  is  increased  by  certain  poisons  (strych- 
nine)  and  during  tetanus.  It  is  greater  in  children  than  in 
adults. 

It  is  decreased  by  certain    poisons     chloroform,  morphine, 


THE  SPINAL    CORD  233 

alcohol).       In   cold-blooded    animals    it  increases  with    the 
temperature. 

Inhibition  of  reflexes. 

1.  Many  reflexes  can  be  inhibited  by  volition.  But  we 
cannot  voluntarily  inhibit  reflexes  which  are  produced  by 
muscles  which  cannot  be  contracted  voluntarily  (e.g.  the 
contraction  of  the  muscles  of  the  uterus,  contraction  of  the 
pupil). 

2.  There  are  special  reflex  inhibition  mechanisms  which 
are  not  dependent  upon  volition. 

It  is  supposed  that  in  man  the  centres  of  such  mechanisms 
lie  in  the  ganglia  of  the  brain,  and  that  from  it  fibres  pass 
down  the  gray  matter  of  the  cord  and  act,  in  a  manner  still 
unknown,  upon  the  cells  so  that  the  reflex  is  inhibited.  If 
the  function  of  these  fibres  is  abolished  by  transverse  section 
of  the  spinal  cord,  the  reflexes  below  the  level  of  the  section 
are  increased. 

In  the  frog  reflex  inhibition  centres  have  been  demon- 
strated in  the  optic  lobes,  the  stimulation  of  which  prevents 
the  reflexes. 

3.  A  reflex  brought  about  by  the  stimulation  of  a  sensory 
nerve  can  sometimes  be  inhibited  by  the  simultaneous  stimu- 
lation of  another  sensory  nerve. 

4.   SPECIAL    REFLEX  CENTRES    IN   THE   SPINAL    CORD 

There  are  in  the  spinal  cord  centres  for  certain  move- 
ments which  can  be  brought  into  activity  reflex  ly. 

(1)  In  the  cervical  region  are  centres  for  the  pupil  reflex: 
(a)   A   centre  for  the   dilation   of  the  pupil,  in  the  upper 

part  of  the  cervical  cord  ; 

($)  A  centre  for  the  constriction  of  the  pupil,  in  the  lower 
part  of  the  cervical  cord. 

This  pupil  reflex  serves  to  regulate  the  amount  of  light 
entering  the  eye.      For  details  see  page  267. 

(2)  In  the  lumbar  region: 
(a)  Micturition  centre. 


234  HUMAN  PHYSIOLOGY 

The  action  of  the  centre  for  the  sphincter  vesicae  is  tonic. 
During  micturition  the  tonus  of  the  sphincter  is  decreased 
and  the  centre  for  the  detrusor  is  stimulated.  This  process 
is  called  forth  reflexly  by  the  distension  of  the  bladder,  which 
stimulates  the  nerves  of  the  bladder  and  thereby  reflexly 
stimulates  the  detrusor  and  inhibits  the  sphincter. 

(b)  Defalcation  centre. 

The  tonus  of  the  centre  of  the  sphincters  ani  is  inhibited 
reflexly  (by  stimulation  of  centripetal  nerves  in  the  rectum 
by  the  accumulated  feces) ;  peristaltic  movements  of  the 
intestine  are  set  up  which,  together  with  the  pressure  of  the 
abdominal  walls,  remove  the  faeces. 

(c)  Centre  for  the  erection  of  the  penis,  ejaculation,  par- 
turition (see  third  section). 


CHAPTER    XVIII 
THE    BRAIN 

1.    CONDUCTING    TRACTS 

The  physiological  significance  of  all  the  details  of  the  course  of 
the  fibres  in  the  brain  which  anatomy  has  demonstrated  is  not 
known.  It  is  therefore  sufficient  for  us  to  describe  the  chief  con- 
ducting tracts. 

I.   Course  of  the  tracts  from  the  spinal  cord  into  the  brain. 

A.  The  motor  tract. — The  crossed  pyramidal  tract  forms 
in  the  medulla  oblongata  the  so-called  decussation  of  the 
pyramids,  breaking  through  the  anterior  horn  on  its  side 
into  the  anterior  ground  bundle  of  the  other  side  and  joining 
the  direct  pyramidal  tract.  From  this  point  upward,  the 
two  pyramidal  tracts  accompany  each  other,  passing  through 
the  pons,  where  they  are  crossed  by  cross  fibres  from  the 
cerebellum,  then  through  the  centre  of  the  crusta  cerebri, 
the  posterior  limb  of  the  inner  capsule,  and  the  corona 
radiata,  to  the  cortex  of  the  cerebral  hemispheres. 

On  its  course  from  the  cerebrum  to  the  decussation,  the 
common  pyramidal  tract  gives  off  fibres  to  the  cells  of  the 
motor  fibres  of  the  cranial  nerves.  The  fibres  of  the  pyramids 
which  come  from  both  sides  cross  shortlv  before  entering-  in 
the  nerve  nuclei  to  which  they  go. 

B.  The  sensory  tracts. 

Go//  's  column,  in  the  medulla  called  the  funiculus  gracilis, 
ends  mainly  in  cells  of  the  nucleus  of  the  funiculus  gracilis. 
From  there,  fibres  penetrate  forward  through  the  gray  sub- 
stance and  cross  the  fibres  from  the  other  side  above  and 
behind  the  decussation  of  the  pyramids.      This  crossing  is 

235 


236  HUM4N  PHYSIOLOGY 

called  the  decussation  of  the  fillet.  After  crossing,  the  fibres 
lie  dorsal  to  the  pyramidal  tracts ;  the)'  then  join  the  sensory 
fibres  which,  having  perhaps  already  crossed  in  the  cord, 
run  upward  in  the  lateral  bundles.  The  common  sensory 
tract  thus  formed,  called  fillet,  passes  upward  through  the 
pons  and  the  crura  cerebri.  Thence  a  part  of  the  fibres  go 
to  the  ganglia  of  the  corpora  quadrigemina ;  another  part, 
crossing  the  ventro-lateral  nucleus  of  the  thalamus  opticus, 
pass,  always  posterior  to  the  pyramidal  tract,  through  the 
posterior  limb  of  the  internal  capsule  into  the  corona  radiata 
to  the  cortex  of  the  cerebral  hemispheres. 

In  their  course  the  fillets  receive  fibres  originating  from 
masses  of  cells  in  which  the  sensor}-  cranial  nerves,  after 
entering  the  brain,  end;  these  fibres  cross  before  joining  the 
fillet. 

The  nuclei  of  the  motor  and  sensory  cranial  nerves  lie  in  the 
upward  prolongation  of  the  gray  matter  which  forms  the  floor  of 
the  fourth  ventricle  and,  above  it,  the  aqueduct  of  Silvius.  The 
(  ranial  nerves,  except  the  optic  and  olfactory,  are  analogous  to  the 
spinal  nerves.  The  optic  nerve  originates  from  the  group  of  ganglia 
in  the  anterior  lobe  of  the  corpora  quadrigemina  and  the  lateral 
geniculate  bodv.  The  olfactory  nerve  proceeds  directly  from  the 
cerebral  hemispheres. 

2.  The  direct  cerebellar  tracts  pass  through  the  restiform 
body  [inferior  cerebellar  peduncle]  to  the  cerebellum,  where 
they  end  in  the  gray  matter  of  the  worm.  Besides  this  con- 
nection of  the  cerebellum  with  the  spinal  cord  there  are- 
other  fibres  which  unite  the  cerebellum  with  the  cerebral 
hemispheres.      They  are: 

{a)  Fibres  which  pass  from  the  anterior  and  posterior 
cortex  of  the  cerebral  hemispheres  through  the  anterior  and 
posterior  limbs  of  the  internal  capsule  and  the  crura  cerebri 
to  the  nuclei  of  the  pons.  Thence  they  proceed  backward 
to  the  cerebellum  through  the  middle  peduncle  of  the  cere- 
bellum— frontal,  temporal,  and  occipital  regions  being  thus 
joined  to  the  cerebellum. 

(/;)  Fibres  which  proceed  from  the  cerebral  hemispheres 
and,  with  the  fillet,  pass  through  the   thalamus  opticus  into 


THE  BRAIN  237 

the  red  nucleus  of  the  crura  cerebri ;  thence  to  the  other  side 
through  the  pedunculi  cerebelli  into  the  cerebellum. 

C.  The  short  tracts  of  the  spinal  cord,  which  must  be 
regarded  as  reflex  tracts  and  which  run  in  the  anterior 
ground  bundle  and  the  Burdach  column,  cannot  be  traced 
as  separate  tracts  in  the  brain.  There  are  also,  no  doubt, 
many  such  pathways  in  the  brain  which  connect  the  nerve 
cells  and  serve  as  reflex  tracts,  for  in  the  brain  many  reflex 
processes  take  place. 

II.  In  the  cerebral  hemispheres  there  are  still  a  great 
many  fibres  which  connect  various  parts  of  the  cerebral 
hemispheres  with  each  other.      These  are: 

(1)  Fibres  in  the  corona  radiata  to  the  large  ganglia  of 
the  base  (thalamus  opticus,  nucleus  lenticularis,  nucleus 
candatus). 

(2)  The  association  fibres,  by  which  various  parts  of  the 
right  and  left  half  of  the  cerebral  cortex  lying  on  the  same 
side  are  connected  with  each  other. 

(3)  The  commissural  fibres  which  unite  the  right  and  left 
half  of  the  cerebral  cortex.  They  pass  through  the  corpus 
'Callosum  and  the  anterior  commissure. 

The  association  and  commissural  fibres  are  the  conducting 
paths  in  psycho-physical  processes  which  are  the  bases  of 
the  psychical  phenomena  (the  utilizing  of  the  sensation  in 
formation  of  concepts,  etc.). 

2.    CENTRES    IN   THE   MEDULLA    OBLONGATA 

The  medulla  oblongata  is  a  part  of  the  central  nervous 
•system  which  is  of  special  importance  for  the  maintenance 
of  life.  It  contains  the  centres  for  the  regulation  of  certain 
processes  which  provide  for  the  maintenance  of  normal 
metabolism  (centres  for  respiration,  circulation,  and  the 
movements  and  secretions  of  the  alimentary  canal).  The 
great  importance  of  these  centres  for  the  life  of  the  animal  is 
apparent  from  the  fact  that  destruction  of  the  medulla  oblon- 
gata is  immediately  followed  by  death,  while  the  destruction 


238  HUMAN   PHYSIOLOGY 

of  other  centres  of  the  central  nervous  system  is  not  directly- 
fatal.  The  centres  of  the  medulla  oblongata  have  already 
been  mentioned  in  the  chapter  on  metabolism  and  their 
properties  have  there  been  described  in  detail,  so  that  a 
simple  enumeration  will  suffice  here. 

1.  The  respiratory  centre  (see  page  83).  By  this 
centre  the  muscles  which  cause  alternate  inspiration  and 
expiration  (the  diaphragm  and  the  external  intercostal  for 
inspiration,  the  internal  intercostal  for  expiration)  are  stimu- 
lated in  an  orderly  manner.  Its  activity  is  dependent  upon 
the  need  of  oxygen  by  the  body,  for  lack  of  oxygen  and 
accumulation  of  carbon  dioxide  in  the  blood  act  as  normal 
stimuli  for  respiration.  Reflexly  the  respiratory  centre  is 
regulated  by  centripetal  nerves,  namely,  the  fibres  of  the 
vagus  leading  from  the  lungs  to  the  centre.  The  inspiratory 
fibres  of  the  vagus  are  stimulated  during  expiration,  while  the 
expiratory  fibres  are  stimulated  during  inspiration. 

2.  The  centres  for  the  organs  of  circulation  (see  page 
74).      These  are : 

(ez)  The  cardio-inhibitory  centre  (of  the  inhibitory  vagus 
fibres). 

(/;)  The  centre  for  the  sympathetic  nerve  from  the  cervical 
and  the  first  thoracic  ganglia,  which  carry  the  accelerating 
fibres  to  the  heart. 

(c)   The  centre  for  the  constriction  of  blood  vessels. 

(c/)   The  centre  for  the  dilation  of  the  blood  vessels. 

These  centres  serve  to  regulate  the  pressure  of  the  blood 
stream  and  its  distribution  in  the  various  parts  of  the  body 
according  to  existing  needs,  by  means  of  changes  in  the 
number  and  strength  of  the  heart-beats  and  in  the  tonus  of 
the  muscles  of  the  blood  vessels. 

The  cardio-inhibitory  centre  and  the  vaso-constrictor 
centre  are  tonic.  They  are  stimulated  by  lack  of  oxygen 
and  accumulation  of  carbon  dioxide  in  the  blood.  It  appears 
that  this  stimulation  serves  to  protect  the  heart  from  too 
speed)-  exhaustion  during  asphyxia,  by  decreasing  its 
activity,  and  to  compensate  the   resulting  reduction  in  blood 


THE  BRAIN  239 

pressure  by  increasing"  the  tonus  of  the  muscles  of  the 
vessels. 

The  cardio-accelerating  centre  is  also  supposed  to  be 
tonic. 

In  general,  the  centres  for  the  organs  of  circulation  bring 
about  many  reflex  actions.  This  is  clearly  apparent  from 
the  many  and  various  actions  by  which  these  centres  regu- 
late the  distribution  of  blood  according  to  the  needs  of  the 
body. 

3.  Centres  for  certain  movements  and  secretions  of  the 
alimentary  canal  (see  Chapters  VII  and  IX).      These  are: 

(a)  Centres  for  biting,  sucking,  mastication,  deglutition, 
vomiting,  and  perhaps  also  for  the  movements  of  the  stomach 
and  intestines. 

The  centres  of  biting,  sucking,  and  mastication  are  volun- 
tarily stimulated  by  the  cerebral  hemispheres ;  the  other 
centres  are  not  subject  to  the  will.  Deglutition  takes  place 
reflexly  when  the  food  has  been  pushed  from  the  tongue 
behind  the  anterior  pillars  of  the  soft  palate.  ' '  Empty 
swallowing  "  is  made  possible  by  the  swallowing  of  saliva; 
without  saliva  it  is  impossible.  The  vomiting  centre  is  not 
only  stimulated  reflexly,  but  can  also  be  stimulated  by 
psychical  influence  (sight  of  nauseous  objects). 

(b)  Centre  of  salivary  secretion,  perhaps  also  for  gastric, 
intestinal,  and  pancreatic  secretions. 

The  stimulation  of  these  centres  takes  place  involuntarily, 
chiefly  reflexly  by  the  introduction  of  food  in  the  alimentary 
canal ;  sometimes  also,  by  psychical  influences,  sight  of 
tempting  food  stimulates  salivary  and  gastric  secretion. 

4.  Centres  for  the  secretion  of  sweat  and  tears  (see  pages 
\  109  and  1 10). — These  centres  also  are  not  stimulated  volun- 
tarily. The  perspiration  centre  is  directly  stimulated  by  the 
raising  of  the  temperature  (heat)  and  also  by  lack  of  oxygen 
and  the  accumulation  of  carbon  dioxide  in  the  blood 
(asphyxia).  Its  activity  is  influenced  by  psychical  condi- 
tions (sweat  of  fear). 

The  stimulation  of  the  centre  for  lachrymal  secretion  takes 


240  HUMAN  -PHYSIOLOGY 

place    reflexly  by  stimulation    of   the    conjunctival    nerves, 
by  strong  light,  and  by  psychical  influences  (weeping). 

5.  In  the  medulla  oblongata  is  situated  a  spot  which  is 
connected  with  the  glycogen  and  sugar  formation  in  the  liver 
(see  page  146).  Destruction  of  this  centre  (Piqure)  causes 
diabetes  mellitus. 

6.  It  is  supposed  that  there  exists  in  the  medulla  oblon- 
gata a  centre  which  governs  the  reflex  centres  in  the  spinal 
cord  and  binds  these  centres  together.  It  is  supposed  to 
be  stimulated  by  lack  of  oxygen  and  accumulation  of  carbon 
dioxide  in  the  blood,  whereby  convulsion  of  all  the  muscles 
in  the  body  (asphyxia  convulsion)  is  produced.  Hence  this 
centre  is  also  called  the  centre  of  convulsion. 

:;.  CENTRES  IN  THE  CEREBELLUM,  PONS,  CORPORA 
QUADRIGEMINA,  AND  THE  BASAL  GANGLIA*  OF 
THE    CEREBRAL   HEMISPHERES 

The  centres  here  located  serve,  as  far  as  we  are  acquainted 
with  their  functions,  to  coordinate  the  movements  of  the 
skeletal  and  eye  muscles.  They  may  be  divided  into  two 
groups. 

1 .  Centres  for  the  coordinated  compensatory  movements 
maintaining  the  equilibrium  of  the  body. — These  centres 
bring  about  a  series  of  complicated  orderly  movements  of 
the  muscles  so  that  the  body  keeps  its  equilibrium.  When, 
for  example,  during  standing  or  walking  the  equilibrium  of 
the  body  is  destroyed  so  that  the  body  threatens  to  fall,  the 
centres  call  forth  such  compensatory  movements  of  the  body 
muscles  that  the  equilibrium  and  the  normal  position  are 
regained.  When  the  disturbance  of  the  equilibrium  is  great, 
these  actions  can  be  readily  observed,  but  these  compensa- 
tory movements  also  take  place  when  the  position  of  the 
body  deviates  but  little  from  the  normal  position.  In  this 
case  the  movements  are  less  apparent  and  made  so  uncon- 
sciously that  our  attention   is  called  to  them  only  in  certain 

*  The  basal  ganglia  arc  the  thalamus  opticus,  nucleus  caudatus,  and  the 
nucleus  lenticularis. 


THE  BRAIN  241 

diseases.  The  centripetal  nerves  which  acquaint  these 
centres  with  the  position  of  the  body  are : 

(a)  The  sensory  nerves  of  the  entire  body  which  end  in 
the  muscles,  tendons,  and  joints  and  which  notify  the  centre 
of  the  relative  position  of  individual  members  to  each  other 
and  of  the  extent  of  the  tension  of  the  muscles. 

(£)  The  optic  nerve,  which,  by  means  of  visual  perception, 
acquaints  the  centre  with  the  position  of  the  body  with  refer- 
ence to  the  objects  of  the  external  world. 

(c)  Certain  fibres  of  the  auditory  nerve  which  end  in  the 
semicircular  canals  of  the  internal  ear.  These  semicircular 
canals  are  sense  organs  for  ascertaining  the  position  and 
movements  of  the  head. 

In  the  execution  of  compensatory  movements  all  the 
skeletal  muscles  take  part. 

As  to  the  position  of  the  centres,  it  is  supposed  that  the 
coordinated  movements  of  the  lower  extremities  which  chiefly 
function  in  locomotion  and  standing  are  governed  by  the 
cerebellum.  The  centres  in  the  corpora  quadrigemina  are 
supposed  to  regulate  chiefly  the  movements  of  the  arms  and 
hands. 

Nothing  is  definitely  known  in  detail  concerning  the  posi- 
tion and  limits  of  the  centres.  This  is  not  surprising  when 
it  is  borne  in  mind  that  in  these  centres  the  greater  part  of 
all  the  sensory  and  motor  nerves  are  connected. 

If,  because  of  pathological  changes  and  disturbances,  interrup- 
tions in  the  connections  between  the  afferent  and  efferent  nerves 
for  these  centres  or  in  the  centres  themselves  take  place,  a  disturb- 
ance in  the  coordinated  movements  of  the  body  results.  Hence 
in  locomotor  ataxia,  in  which  the  sensory  nerves  of  the  lower  limbs 
are  paralyzed,  uncoordinated  movements  are  made  during  walking. 
A  person  suffering  with  locomotor  ataxia  cannot  stand  erect  when, 
by  closing  his  eyes,  he  deprives  himself  of  the  only  remaining 
means  of  orientating  himself. 

It  is  also  possible  that  each  centre  or  its  tract  o'n  one  side  only  may 
be  paralyzed  or  abnormally  stimulated  by  disease.  The  result  is 
that  the  strength  of  the  stimulation  which  is  unconsciously  imparted 
to  the  muscles  is  not  equal  on  both  sides.  This  results  in  abnormal 
positions  and  movements  of  the  body,  called  forced  position  and 
forced  movements  because  they  are  called  forth  involuntarily,  indeed 


242  HUMAN  PHYSIOLOGY 

against  the  will.  Forced  movements  in  animals  are,  for  example, 
the  circus  movements,  clock-hand  movements,  rolling  movements. 
In  normal  individuals  forced  movements  may  be  observed  during 
dizziness  caused  by  rotation. 

2.  Centres  for  the  movements  of  the  eyes. — All  the 
centres  for  the  movements  of  the  eyes  lie  in  the  gray  matter 
forming  the  floor  of  the  aqueduct  of  Silvius  and  the  fourth 
ventricle  (except  the  centre  for  closing  the  eyelid  and  the 
pupil  reflex,  see  below  and  page  233). 

(<?)  The  centres  for  the  coordinated  movements  of  both 
eyes. — Concerning  the  functions  of  the  individual  centres, 
Ese  page  280.  Reflexes  brought  about  by  means  of  these 
centres  are : 

1.  Involuntary  movements  of  the  eye  (afferent  impulse 
travelling  through  the  optic  nerve)  by  which  the  eye  follows 
a  moving  object  or  by  which  the  glance  is  thrown  upon  a 
luminous  object. 

2.  Reflexes  which   are  called  forth   by  the  sense  organs 

for    perceiving    the    position    and    movements    of   the    head 

(semicircular  canals  of  the  ear,  the  centripetal   nerve  being 

the    auditory).      In    this    group    belong    the    compensatory 

movements  of  the  eyes  which   are   involuntarily  made  when 

the  head    is    moved,    in   order   that  the   line   of  vision    may 

remain  on  fixed  objects. 

Forced  movements  of  the  eye  which  occur  in  diseases  of  these 
centres  and  their  paths  are  called  nystigmus. 

(/>)  Centre  for  the  common  innervation  of  accommodation, 
convergence,  and  contraction  of  the  pupil.  This  is  voluntarily 
stimulated  during  near  vision. 

if)  Centre  for  the  closing  of  the  eyelids.  This  is  volun- 
tarily or  reflexly  stimulated.  Reflex  stimulation  occurs 
when  the  cornea  or  conjunctiva  is  touched  (centripetal 
nerve  is  the  first  branch  of  the  trigeminus),  or  by  stimulation 
of  the  optic  (blinking).  The  centrifugal  nerve  is  the  facial 
which  innervates  the  palpebrarum  orbicularis.  The  centre 
is  situated  in  the  medulla  oblongata. 

Centres  for  the  regulation  of  body  temperature.  It  is  supposed 
by  some  authors  that  at  the  boundary  between  the  medulla  and  the 


THE  BRAIN  243 

pons  and  in  the  basal  ganglia  there  are  centres  which  regulate  the 
body  temperature  (see  page  181),  but  the  existence  of  these  cen- 
tres has  never  been  definitely  demonstrated. 

Concerning  the  functions  of  the  pineal  gland  nothing  is 
known.      It  is  regarded  as  a  rudimentary  eye. 

4.   FUNCTIONS  OF  THE  CEREBRAL  CORTEX 

Psycho-physical  processes  take  place  in  the  cells  of  the 
cerebral  cortex.  The  cerebral  cortex  is  the  seat  of  intelli- 
gence. Human  beings  in  which  the  cortex  of  the  cerebral 
hemispheres  has  been  destroyed  by  disease,  or  animals  in 
which  it  has  been  extirpated,  are  stupid  ;  they  take  no  notice 
of  the  external  world,  flee  from  no  danger,  do  not  independ- 
ently seek  their  food,  but  they  still  manifest  all  the  reflex 
movements  the  centres  for  which  are  located  in  the  lower 
parts  of  the  brain  and  spinal  cord.  In  the  animal  world,  the 
cerebral  hemispheres  and  the  number  of  the  convolutions 
vary  with  the  degree  of  intelligence. 

The  question  whether  the  various  psychical  processes 
(sensations,  thought,  will)  are  localized  in  various  definite 
parts  of  the  cerebral  cortex  or  whether  all  the  parts  of  the 
cortex  have  the  same  value  in  psychical  processes  is  at 
present  variously  answered  by  different  authors.  In  higher 
animals  (monkeys  and  dogs)  it  has  been  attempted  to 
localize  the  functions  of  the  cerebral  hemispheres  in  two 
ways :  either  by  observing  the  results  of  the  stimulation  of  a 
definite  part  of  the  cerebral  cortex,  or  by  studying  the  dis- 
appearance of  functions  after  removal  of  such  a  definite  part. 

By  the  first  method  it  has  been  found  that  in  the  cortex 
there  are  a  number  of  definite  areas  the  stimulation  of 
which  is  always  followed  by  the  contraction  of  a  definite 
group  of  muscles.  These  areas,  called  motor  areas,  are,  in 
general,  situated  in  the  central  convolutions. 

It  is  noteworthy  that,  under  certain  circumstances,  stimulation 
of  the  cortex  is  followed  simultaneously  by  the  contraction  of  a 
certain  group  of  muscles  and  the  relaxation  of  the  corresponding 
antagonistic  muscles. 


244  HUMAN   PHYSIOLOGY 

Partial  extirpation  often  results  in  the  temporal-}-  dis- 
appearance of  functions,  but  after  some  time  these  functions 
reappear. 

The  results  of  experiments  in  stimulation  and  extirpation 
have  been  variously  interpreted.  The  adherents  to  the 
localization  theory  hold  that  the  effect  of  stimulation  is  pro- 
duced by  the  stimulation  of  the  motor  centres  which  arc 
employed  in  executing  voluntary  movements  ;  the  opponents 
of  this  theory  hold  that  by  this  stimulation  we  do  not  really 
stimulate  the  centres,  but  the  motor  fibres  which  pass  through 
the  stimulated  spot.  The  disappearance  of  a  function  by 
extirpation  and  the  subsequent  reappearance  of  that  function 
depend,  according  to  the  adherents  of  the  localization 
theory,  upon  the  fact  that  the  centre  in  which  the  function 
is  located  has  been  removed,  but  that  subsequently  other 
centres  have  gradually  taken  up  this  function.  In  the  re- 
appearance of  the  function  after  partial  extirpation  the 
opponents  of  the  localization  theory  find  support  for  their 
position  that  the  psychical  functions  are  not  definitely- 
localized.  The  first  disappearance  of  the  function  they  re- 
gard as  due  to  the  inhibitory  influences  caused  by  the  injury 
[Hemmungserscheinungen]. 

Although  at  present  the  views  concerning  the  localization 
of  functions  in  the  cerebral  cortex  of  animals  arc  at  variance, 
yet  there  are  many  observations  which  render  it  almost 
certain  that  in  man  there  is,  to  a  certain  extent,  a  localiza- 
tion of  the  psychical  functions  in  the  cerebral  hemispheres. 

The  theory  of  the  psychological  topography  of  the  human 
cerebral  cortex  is  based  upon : 

(i)  Anatomical  and  embryolo<;ical  investigations  on  the 
course  of  fibres,  by  which  parts  of  the  cerebral  cortex  are 
connected  with  each  other  as  well  as  with  other  parts  of  the 
central  nervous  system. 

(2)  Upon  clinical  observations  in  connection  with  the 
results  of  pathological  anatomical  investigations. 

Topography  of  the  cerebral  cortex  of  man. —  The  cere- 
bral cortex  of  man  may  be  divided  into: 


THE   BRAIN 


245 


I.  Sensory  areas,  i.e.  centres  in  which  the  conscious  sen- 
sations are  formed.      There  are  four  such  areas. 

(1)  Centres  for  ordinary  and  tactile  sensations. — These 
lie  in  the  anterior  and  posterior  central  gyri,  the  posterior 
parts  of  the  frontal  lobe,  the  paracentral  lobe,  and  the  gyrus 
fornicatus  (compare  Figs.  21-24). 


Fig.  21. 


Fig.   22. 
Convolutions  of  the  Cerebral  Hemispheres. 

The  centripetal  fibres  of  the  corona  radiata  of  the  tactile 
centres  are  the  indirect  processes  of  the  posterior  roots 
(fibres  of  the  fillet  and  anterior  peduncle  which  pass  through 
the  ventro-lateral  nucleus  of  the  thalamus  opticus  and  thence 
into  the  corona  radiata).  In  this  area  the  sensations  of  the 
skin  and  organs  are  perceived. 


246 


HUMAN  PHYSIOLOGY 


We  do  not  exclude  the  possibility  that  some  of  the  indefinite 
organ  sensations  are  perceived  in  centres  situated  lower  down  in 
the  brain. 

(2)  The  auditory  centre  lies  in  the  median  and  the  pos- 
terior part  of  the   upper  temporal   convolution,    and   in  the 


Tactile  area. 


Pa  1  u 
associatiun-centre 


Olifactory  area. 


Association  centre  of 
the  occipito-tetnporal  lube. 


FlG.    24. 

Sensory  Areas  of  the  Cerebral  Cortex. 

The  sensory  areas  are  dotted.  In  Fig.  23  the  temporal  lobe  is  slightly  drawn 
downward  in  order  to  show  the  auditory  centre.  The  island  of  Reil  is  seen  at 
the  shaded  portion. 

transverse   convolutions   of  the   temporal   lobes.      The    cen- 
tripetal   corona    radiata  fibres  of  the  auditor)-  centre  are  the 


THE  BRAIN  247 

indirect  continuations  of  the  cochlear  nerve  (through  the 
lateral  fillet  and  the  internal  geniculate  bod}'  to  the  corona 
radiata).  The  nervus  vestibularis  is  supposed  to  be  con- 
nected with  the  centres  for  ordinary  and  tactile  sensations, 
not  with  the  auditor}-  centre. 

(3)  The  visual  centre  lies  in  the  cuneus,  angular  gyrus, 
and  occipital.  Their  centripetal  corona  radiata  fibres  lie  in 
the  optic  radiation  of  Gratiolet  (continuation  of  the  optic 
tract  through  the  external  geniculate  body  and  anterior 
corpora  quadrigemina  into  the  corona  radiata). 

4  The  olfactory  centre  lies  in  the  basis  of  the  cortex  of 
the  frontal  lobe,  in  the  basal  portion  of  the  gyrus  fornicatus, 
the  island  of  Reil,  the  uncus,  and  the  inner  part  of  the  tem- 
poral lobes. 

The  position  of  the  centre  of  taste  is  not  yet  known. 

II.  Motor  areas  are  centres  by  which  the  voluntary 
movements  are  inaugurated.  The}-  lie  in  the  same  portion 
of  the  cortex  as  the  centres  for  tactile  sensations.  Their 
centrifugal  corona  radiata  fibres  are  the  pyramidal  tracts  the 
origin  of  which  lies  in  the  central  convolution.  In  the 
upper  part  of  this  convolution  originate  the  motor  fibres  for 
the  lower  extremities;  in  the  median,  those  for  the  upper 
extremities;  and  in  the  lower  portion,  those  for  the  face.  In 
the  posterior  part  of  the  lower  frontal  convolution,  generally 
in  the  left  cerebral  hemisphere,  are  situated  the  motor 
centres  for  the  muscles  which  function  in  the  production  of 
voice  and  speech  ('motor  speech  centre). 

It  is  supposed  that  motor  cells  are  also  found  in  other  sensory 
areas,  but  this  is  not  agreed  upon  by  all  authors. 

III.  Those  parts  of  the  cerebral  cortex  which  do  not 
belong  to  the  sensor}-  or  motor  areas  form,  according  to  a 
new  theory,  the  association  centres.  These  centres  func- 
tion in  the  formation  of  concepts  from  the  sense  percepts. 
This  view  is,  however,  rejected  by  many  authors. 

It  is  supposed  that  the  association  centres  differ  anatomically 
from  the  other  centres  in  the  following  respects.     The  association 


24S  HUMAN    PHYSIOLOGY 

centres  are  supposed  to  be  connected  with  each  other  and  with  the 
sensory  areas  chiefly  by  association  and  commissural  fibres,  and  to 
contain  relatively  few  corona  fibres  connecting  it  with  the  lower 
parts  of  the  brain.  The  larger  part  of  the  fibres  from  the  corona 
radiata  are  supposed  to  proceed  to  the  sensory  and  motor  areas. 
Moreover,  the  individual  sensory  areas  are  supposed  not  to  be  con- 
nected with  each  other  by  the  association  fibres,  but  only  with  the 
association  centres. 

Nothing  is  known  concerning  the  nature  of  the  psycho- 
physical processes  which  underlie  psychical  phenomena. 
Up  to  the  present  time  the  investigations  of  these  processes 
have  been  limited  to  their  duration. 

Reaction  time  is  the  time  elapsing  between  the  beginning 
of  the  action  of  a  sense  stimulation  and  a  most  rapidly 
executed  muscular  movement,  e.g.  of  a  finger.  Both  these 
times  are  registered. 

The  measurements  of  the  reaction  time  are: 

For  optical  stimulation 0.15— 0.22  second. 

"    auditory         "  O.  12-O.  18 

"    tactile  "  O.09-O.19 

"    taste  "  o.  16-O.22 

The  reaction  time  is  smaller  for  areas  which  are  more  frequently 
stimulated,  e.g.  the  yellow  spot,  the  tip  of  the  finger,  than  fur 
areas  less  frequently  stimulated,  as  the  periphery  of  the  retina,  skin 
of  the  arm.  It  is  also  dependent  upon  the  degree  of  attention  and 
practice,  and  upon  the  psychical  attitude.  Individual  peculiarities 
also  influence  the  reaction  time. 

When  a  very  accurate  registration  of  time  must  be  made,  for  in- 
stance by  a  person  noting  the  passage  of  a  star  across  the  thread 
of  a  telescope,  the  reaction  time  must  be  taken  into  consideration. 
The  individual  variations  of  the  reaction  time  are  brought  into 
account  by  astronomers  as  "  personal  equation." 

The  more  complex  the  psychical  processes  which  intervene 
between  the  sense  stimulation  and  the  reaction,  and  the 
longer  the  time  necessary  for  reflection,  the  greater  will  be 
the  length  of  time  between  the  beginning  of  stimulation  and 
the  reaction. 

The  elucidation  of  the  psychical  phenomena  themselves  1  sensa- 
tion, thought,  volition,  attention,  memory,  etc.  )  is  the  object  of 
IVychology. 


THE  BRAIN  249 

The  interruption  of  psychical  functions  by  sleep  can  be 
accounted  for  by  the  rest  of  the  nerve  cells  of  the  cerebral 
cortex.  How  this  rest  is  brought  about  is  not  known.  The 
supposition  that  cessation  in  the  activity  of  the  cells  is  due 
to  fatigue  or  lack  of  blood  in  the  cells  of  the  brain  does  not 
explain  all  the  phenomena  of  sleep.  Sleep  also  depends 
upon  the  stimulation  of  the  sense  organs.  A  person  can 
be  made  to  sleep  by  withdrawing  the  stimulation  of  the 
senses  as  far  as  possible.  Customary  sensations  do  not  dis- 
turb sleep,  strange  sensations  do.  Sometimes  the  cessation 
of  customary  sensations  awakes  the  sleeper.  (The  awaking 
of  the  miller  when  the  mill  stops.) 

During  sleep  only  the  functions  of  the  cerebral  hemispheres 
cease  ;  the  other  centres  of  the  central  nervous  system  (reflex  and 
coordinated  centres)  may  remain  active.  The  eyelids  are  closed 
during  sleep,  the  eyes  are  turned  inward  and  upward,  the  pupils 
are  contracted,  respiration  is  slower.  Metabolism  is  less  during 
sleep  than  during  waking  hours. 

Dreams  are  due  to  less  profound  sleep.  Somnambulism  and  hyp- 
notism are  abnormal  conditions  of  partial  sleep. 

Chemical  composition  and  metabolism  of  the  central  nervous 
organs. — The  whits  substance  of  the  central  nervous  system  con- 
tains 31$  solids,  including  proteid  and  collagen  8$,  lecithin  3$, 
cholesterin  and  fat  15$,  protagon  3$;  besides  these,  some  substances 
containing  nitrogen  and  phosphorus  insoluble  in  ether  (nuclein, 
neuro-keratin,  jecorin)  1.5$;   salts  0.2$. 

The  gray  substance  contains  18$  solids,  including  proteid  and 
collagen  10$,  lecithin  3$,  cholesterin  and  fat  3.5$,  cerebrin  and 
substances  insoluble  in  ether  1$,  salts  0.5$. 

Nothing  is  known  concerning  the  metabolism  in  the  spinal  cord 
and  brain.  Metabolism  is  not  increased  to  an  appreciable  extent 
by  mental  work.  The  abundance  of  blood  in  the  brain  and  the 
fact  that  stoppage  of  blood  supply  paralyzes  the  nerve  cells  in  a  few 
minutes,  indicates  that  the  metabolism  is  very  energetic. 

The  cerebrospinal  fluid  which  surrounds  the  central  nervous  sys- 
tem and  fills  its  cavities  has  a  specific  gravity  of  1.005.  It  con- 
tains 1—1.5$  solids,  in  which  proteids  are  either  absent  or  only 
present  in  traces.  In  it  has  been  found  a  substance  which  reduces 
cupric  oxide  and  appears  to  be  pyrocatechin. 


CHAPTER    XIX 

THE    PERIPHERAL    NERVES    AND    THE    SYMPATHETIC 

SYSTEM 

1.    THE    SPINAL    NERVES 

The  spinal  nerves  leave  the  spinal  cord  by  the  anterior 
and  posterior  roots. 

The  anterior  roots  are  motor,  the  posterior  chiefly  sensor)' 
(Bell's  law),  but  also  contain  a  few  motor  nerves  for  the 
muscles  of  the  intestines. 

The  nerve  fibres  innervating  a  muscle  do  not  all  lie  in  the 
same  motor  root,  but  a  muscle  is  supplied  with  motor  fibres 
from  several  anterior  roots.  These  fibres  join  each  other 
(plexus)  and  then  proceed  in  a  common  trunk  to  the  muscle. 

The  anterior  roots  contain  fibres  whose  simultaneous  stimula- 
tion calls  forth  movements  of  entire  muscle  groups  which  re- 
semble certain  coordinated  movements  frequently  executed  in  life. 
For  example,  stimulation  of  the  first  dorsal  root  in  a  monkey  re- 
sults in  the  movements  of  the  arm  similar  to  those  made  in  pluck- 
ing fruit  ;  stimulation  of  the  seventh  cervical  calls  forth  movements 
of  the  arms  similar  to  those  made  in  climbing  ;  by  stimulation  of 
the  sixth  cervical  the  hand  is  carried  to  the  mouth.  Perhaps  the 
cells  from  which  these  nerves  originate  lie  together  in  special  cell- 
groups  in  the  spinal  cord,  which  may  be  regarded  as  coordinated 
centres.  From  these  centres  the  nerve  fibres  accompany  each 
other  to  the  plexus. 

The  functions  of  the  individual  spinal  nerves  can  be 
learned  from  their  anatomical  connections. 

2.    CRANIAL  NERVES 

I.  The  olfactory  nerve  is  the  nerve  of  smell.  The  olfac- 
tory bulb  is  the  sub-cortical  centre  of  this  nerve ;  in  it  cells 
are  interposed  in  the  tract. 

250 


PERIPHERAL   NERVES  AND    THE  SYMPATHETIC  SYSTEM     251 

II.  The  optic  nerve  is  the  nerve  of  sight.  The  fibres  of 
this  nerve  leave  the  brain  by  the  optic  tract.  Their  nearest 
nuclei  lie  in  the  anterior  corpus  quadrigeminum  and  in  the 
lateral  geniculate  body.  These  parts  are  connected,  on  the 
one  hand,  with  the  cerebral  cortex  by  means  of  fibres  of  the 
corona  radiata  and,  on  the  other  hand,  with  the  more  pos- 
terior nuclei  of  the  brain,  especially  the  nuclei  of  the  nerves 
of  the  eye  muscles.  The  optic  tract  passes  over  into  the 
cJiiasma,  where  a  part  of  the  fibres  cross.  Thence  they  pro- 
ceed to  the  eye  as  the  optic  nerve.  Because  of  this  partial 
crossing  in  the  chiasma,  the  inner  half  of  each  retina  is 
innervated  by  fibres  from  the  opposite  side  of  the  brain,  while 
the  outer  half  receives  fibres  from  the  same  side  of  the  brain. 

III.  The  oculo-motor,  IV.  the  pathetic  (trochlear),  and 
VI.  the  abducent  are  the  motor  nerves  for  the  external  and 
internal  eye  muscles  (except  the  dilator  of  the  pupil)  and 
the  levator  palpebral  superioris.  The  trochlear  innervates 
the  superior  oblique,  the  abducent  the  rectus  externus,  the 
oculo-motor  all  the  other  eye  muscles. 

V.    The  trigeminus  contains : 

t.  Sensory  fibres  for  the  whole  head  except  the  jaws  and 
ears,  which  are  supplied  by  the  glossopharyngeal  and  the 
ramus  auricularis  vagi. 

2.  Motor  fibres  for  the  muscles  of  mastication  (temporal, 
internal  and  external  pterygoid,  and  masseter) ;  also  for  the 
tensor  palati  mollis,  mylohyoid,  the  anterior  belly  of  the 
digastric,  and  the  tensor  tympani. 

3.  Secretory  fibres  for  the  tear  glands. 

The  lingualis  trigemini  nerve  contains  secretory  fibres  (for  the 
submaxillary  and  sublingual  glands)  ;  also  vaso-dilators  and  fibres 
for  taste,  which,  however,  originally  leave  the  brain  in  company 
with  the  facial  and  glossopharyngeal  and  through  the  corda  tympani 
reach  the  lingual.  Besides  these,  the  trigeminus  contains  vaso- 
motor and  secretory  nerves  for  the  sweat  glands  of  the  face,  which, 
however,  are  derived  from  the  sympathetic. 

VII.  The  facial  contains  motor  fibres  for  all  the  face 
muscles,  for  the  stylohyoid  and  the  posterior  belly  of  the 
digastric,  and  for  the   stapedius  muscles.      It  also  contains 


252  HUMAN   PHYSIOLOGY 

fibres  which  reach  the  sphenopalatinum  ganglion  through 
the  petrosus  superficialis  major;  thence  the}'  proceed  to  the 
levator  palati  mollis  and  azygos  uvulae.  Besides  these  the 
facial  contains  secretory  and  vaso-dilator  fibres  which,  in  the 

chorda  tympani,  join  the  lingualis  and  with  this  proceed  to 
the  salivary  glands. 

VIII.  The  auditory  contains,  in  the  nervus  cochlearis, 
the  nerves  of  hearing.  It  also  contains,  in  the  nervus  ves- 
tibularis, fibres  which  proceed  from  the  semicircular  canal 
of  the  internal  ear,  the  organ  of  the  sense  of  equilibrium,  to 
the  brain.  These  fibres  reflexly  influence  the  coordinated 
movements  of  the  bod}-  for  maintaining  its  position  and 
equilibrium. 

IX.  The  glossopharyngeal  contains: 

1 .  Sensory  fibres  for  the  posterior  parts  of  the  tongue, 
pillars  of  the  fauces,  tonsils,  jaw,  and  epiglottis. 

2.  Motor  fibres  for  the  stylopharyngeal  muscles  and  the 
median  pharyngeal  constrictor. 

3.  Nerves  of  taste.  The  nerves  supplying  the  posterior 
part  of  the  tongue  proceed  thither  directly.  Those  supply- 
ing the  anterior  part  pass  from  the  petrosus  ganglion  of  the 
glossopharyngeal  through  the  tympanic  plexus  to  the  genic- 
ulate ganglion  of  the  facial,  thence  the}-  proceed  through 
the  chorda  tympani  to  the  lingual.  It  is  supposed  that  some 
of  the  taste  nerves  of  the  glossopharyngeal  pass  through  the 
tympanic  plexus  and  the  Jacobson's  anastomoses  to  the 
nervus  petrosus  superficialis  minor,  otic  ganglion,  lingual, 
etc. 

4.  Secretory  fibres  which  pass  through  the  Jacobson's 
nerve  and  the  nervus  petrosus  superficialis  minor,  etc.,  to 
the  parotid  glands. 

X.  Vagus  and  XI.  spinal  accessory  form  together  a 
mixed  nerve  whose  centrifugal  fibres  originate  from  the 
accessor}',  and  the  centripetal  from  the  vagus.  The  external 
branch  of  the  accessory  contains  motor  fibres  for  the  sterno- 
cleido-mastoid  and  the  cucullaris  muscle.  The  common 
vago-accessory  send  fibres 


PERIPHERAL    NE RISES   AND    THE   SYMPATHETIC  SYSTEM     253 

(i;    To  the  circulation  apparatus: 

(a)  The  inhibitory  fibres. 

(b)  Sensory  and  reflex-acting  'depressor^  to  the 
heart. 

(2)    To  the  respiratory  apparatus: 

(a  i  Motor  fibres  for  the  muscles  of  the  larynx  (in 
the  superior  laryngeal  for  the  crycothyroid,  in  the 
recurrent  laryngeal  for  the  other  muscles .  and  for  the 
bronchial  muscles. 

(b)  Sensor}*  fibres  for  the  larynx    laryngeal  superior  . 
trachea,  and  lungs. 
(3;   To  the  muscles  of  the  alimentary  canal: 

(a  Motor  fibres  for  the  movement  and  peristalsis  of 
the  esophagus,  stomach,  and  intestine. 

(b)  Sensory  fibres  for  the  esophagus  and  stomach. 
(V)  Secretory  fibres  for  the  stomach    and    probably 
also  for  the  pancreas  and  glands  of  intestine. 
In  addition  to  these  the  vagus  is  supposed  to  contain  fibres 
"which  regulate  the  sugar  formation  in  the  liver. 

XII.  The  hypoglossals  is  the  motor  nerve  for  the  muscles 
of  the  tongue. 

3.    SYMPATHETIC    SYSTEM 

The  sympathetic  nerves  are  connected  with  the  central 
nervous  system  by  the  rami  communicantes,  which  pass  from 
the  trunks  of  the  spinal  nerves  to  the  sympathetic  ganglia. 
The  sympathetic  contains  the  vaso-motor  fibres  for  the  entire 
body.  These  pass  either  directly  to  the  vessels  or  first  join 
the  peripheral  nerves  and,  in  common  with  them,  continue 
their  course.  The  sympathetic  also  sends  secretory  nerves 
to  the  sweat  glands. 

Besides  these  the  sympathetic  contains  : 

(1)  In  the  cervical  region 

(a)  Fibres  for  the  dilation  of  the  pupil. 

(b)  Secretory  fibres  for  the  salivary  and  lachrymal 
glands. 

(c)  Cardio-augmentor  fibres. 


254  HUMAN   PHYSIOLOGY 

(2)   In  the  thoracic  region 

(a)  Cardio-augmentor  fibres  (from  the  first  thoracic 
ganglion). 

(b)  The  splanchnic  nerve,  which  contains  sensory 
nerves  for  the  intestine,  and  inhibitory  nerves  for  the 
peristaltic  movements. 

All  the  motor  fibres  contained  in  the  splanchnic  are  in- 
voluntary.     The  sympathetic  fibres  are  non-medullated. 


CHAPTER    XX 

SENSE    ORGANS    IN    GENERAL 

THE  sense  organs  are  the  apparatus  in  which  the  periph- 
eral sensory  nerves  end  and  which  are  stimulated  by  external 
or  internal  influences.  The  sensory  nerves  take  up  the  im- 
pulse and  carry  it  to  the  central  nerve  organ. 

The  sense  organs  are  built  for  the  reception  of  ' '  ade- 
quate "  stimuli  and  are  generally  acted  upon  by  these. 

The  adequate  stimuli  for  the  eye  are  the  ether  vibrations  of 
certain  length ;   those  for  the  ear  are  certain  vibrations  of  air. 

The  stimulation  of  the  sensory  nerves  produces  sensations 
in  the  cells  of  the  cerebral  cortex  to  which  they  lead. 

The  sensations  may  differ  from  each  other  in  quality  and 
intensity. 

As  differing  in  quality  we  regard,  e.g.,  the  different  sensations 
of  colors,  or  sounds,  or  smell,  etc.  ;  while  the  light  and  dark 
sensations,  or  the  loud  and  low  sound  sensations,  are  regarded  as 
differing  in  intensity. 

Law  of  the  specific  energy  of  the  sensory  nerves. — The 
quality  of  the  sensation  is  constant  for  each  sensory  nerve 
and  is  independent  of  the  nature  of  the  stimulus. 

For  example,  the  stimulation  of  the  optic  nerve  always  causes 
a  sensation  of  light,  whether  the  nerve  be  stimulated  by  the 
adequate  or  by  some  other  stimulus  (mechanical,  electrical). 

In  what  manner  the  specific  energy  of  the  sensor)-  nerve 

is  determined  is  not  fully  known.      We  know  no  differences 

in  the  structure  or  physiological  stimulation  processes  in  the 

nerve  elements  (fibres  and  cells)  which  could  determine  this 

difference  in  the  specific  energy  of  the  sensory  nerves. 

255 


256  HUMAN   PHYSIOLOGY 

It  is  to  be  noticed  that  the  adequate  stimulus  does  not  objec- 
tively contain  the  quality  of  the  sensation  which  it  produces.  For 
example,  the  vibrations  of  ether  which  act  upon  the  eye  have 
nothing  to  do  with  the  notion  of  light.  The  conception  of  light 
consists  only  in  subjective  perception. 

The  intensity  of  the  sensation  is,  other  things  being  equal, 
dependent  upon  the  intensity  of  the  stimulus. 

The  liminal  intensity  of  a  stimulus  is  the  feeblest  stimu- 
lus still  perceptible;  the  "difference-threshold"  of  the 
stimulus  is  the  smallest  perceptible  difference  in  the  intensity 
of  two  stimuli  or  the  smallest  perceptible  change  in  a  stimu- 
lus. The  size  of  the  "difference-threshold  "  varies  with  the 
absolute  strength  of  the  intensity  of  the  stimulus.  The 
smallest  perceptible  change  in  the  intensity  of  the  stimulus  is 
proportional  to  the  absolute  strength  of  the  stimulus — Weber's 
Law. 

According  to  Fechner's  psycho-physical  law,  the  strength  of 
the  sensations  is  related  to  the  strength  of  the  stimuli  as  a 
logarithm  to  its  number.  The  validity  of  Fechner's  law  is  dis- 
puted by  many  authors. 

Objections  have  also  been  made  against  the  general  validity  of 
Weber's  law. 

Besides  differences  in  intensity  and  quality  we  can  discrimi- 
nate between  the  duration  of  sensations,  and  in  some  (sight 
and  tactile)  between  the  space  conditions  (place  and  extent 
of  sensation). 


CHAPTER    XXI 

OPTICS 

THE  adequate  stimuli  for  the  eye  are  certain  vibrations  of 
ether,  called  light  because  they  call  forth  the  sensations  of 
light.  In  order  that  an  object  shall  be  clearly  seen,  rays 
of  light  must  pass  out  from  the  object,  which  by  refraction 
in  the  eye  form  an  inverted  real  image  of  the  object  on  the 
retina.  The  cones  and  rods  are  the  elements  of  sight;  they 
form  a  mosaic  of  nerve  elements  of  which  every  point  upon 
which  light  falls  can  be  stimulated.  Hence  different  object 
points  can,  by  their  stimulation  of  various  retinal  points,  call 
forth  separate  sensations  of  light  and  can  therefore  be  seen 
as  distinct  points. 

1.    DIOPTRIC  MECHANISM 

Physical  observations. 

i.  If  a  ray  of  light  (S,,  Fig.  25)  passes  from  the  medium Mt  into 
another  medium  Af„,  it  is  refracted  at  the  surface  bounding  the  two 
media  (f),  i  e.  it  takes  another  direction  (*S"2).  The  angle  a  which 
St  forms  witli  the  perpendicular  /  upon  the  plane  f  is  called  the 
angle  of  incidence.  The  angle  ft  which  S\  forms  with  /  is  called 
the  angle  of  refraction.  The  sine  of  the  angle  of  incidence 
divided  by  the  sine  of  the  angle  of  refraction  is,  for  any  given 
pair  of  media,  constant,  and  is  called  the  index  of  refraction. 
When  the  index  of  refraction  of  one  medium  is  given,  the  light 
passes  from  the  air  into  that  medium. 

2.  Homocentric  rays,  or  rays  coming  from  one  luminous  point, 
falling  upon  the  spherical  surface  between  two  media,  are  refracted 
so  that  after  the  refraction  they  either  cross  each  other  at  a  point 
(the  real  image  point)  or,  prolonged  backward,  unite  in  a  virtual 
image  point.      This  is  strictly  true  only  for  a  part  of  a  bundle  of 

257 


258 


HUMAN   PHYSIOLOGY 


light,  namely,  for  those  rays  which  are  approximately  perpendicular 
to  the  surface. 

3.  In  refraction  at  a  spherical  surface  the  following  equation 
expresses  the  distance  of  the  luminous  and  image  point  from  the 
surface  : 


-  +  - 
a.        a_ 


! 

r 


in  which   ;/i   is  the  index  of  refraction  of  the  first  and  »a  that  of 
the   second   medium  ;  r  is  the  radius  of  the  spherical  surface ;   al 

1 


M, 


M, 


Fig.  2s. 


the  distance  of  the  luminous  point ;  at  that  of  the  image  point. 
In  this  formula  r  is  positive  when  the  convexity  of  the  surface  is 
towards  the  side  of  the  luminous  point,  negative  when  it  is  con- 
cave with  respect  to  the  luminons  point,  a.  is  positive  when  the 
rays  entering  are  divergent,  that  is,  come  from  a  real  object  or  lumi- 
nous point  ;  negative  when  the  rays  are  convergent,  that  is,  pass 
to  a  virtual  object  point.  <za  is  positive  for  a  real,  negative  for  a 
virtual,  image  point.  In  Fig.  26,  in  which  O  is  the  luminous  point 
and  C  the  centre  of  curvature,  all  the  values  are  positive.  By 
means  of  the  formula  the  position  of  the  image  for  a  given  posi- 
tion of  the  luminous  point  can  be  found.  The  formula  also  teaches 
that  an  object  or  luminous  point  placed  in  the  image  point  B  has 
its  image  in  the  position  of  the  previous  luminous  point  O.  Two 
points,  of  which  the  one  as  image  point  has  the  other  for  its  object 
point,  are  called  conjugated  points. 

The  direction  of  the  image  point  from  a  given  luminous  point  is 
found  by  drawing  a  straight  line  from  the  luminous  point  through 
the  centre  of  curvature  C.  This  straight  line  is  called  the  chief  or 
directing  ray,  and  the  centre  of  curvature  is  called  the  crossing 


OPTICS 


259 


point  of  the  directing  rays,  or  the  nodal  point.  The  chief  ray 
drawn  through  the  vertex  of  the  refracting  surface  is  called  the 
optical  axis. 


Fig.   26. 


4.  Rays  parallel  with  the  optical  axis  may  be  regarded  as  coming 
from  an  infinitely  distant  object  point  lying  in  the  axis.  After 
refraction  they  unite  at  a  point  on  the  optical  axis,  called  the 
second  focal  point;  its  distance  from  the  surface  is  called  the 
second  focal  distance.  Rays  which,  after  refraction,  run  parallel  to 
the  optical  axis,  pass,  before  refraction,  through  the  first  focal 
point,  whose  distance  from  the  surface  is  called  the  first  focal  dis- 
tance. As  in  the  formula  for  this  case  ai  or  an  is  cc  ,  the  focal  dis- 
tances designated  by/"„  and/j  are 


/.= 


»,  X  r 


/, 


«,  X  r 


The  vertical  planes  erected  upon  the  optical  axis  at  the  focal 
points  are  called  the  focal  planes. 

5.    Construction  of  the  image  of  a  given  object. 

Let  mm  (Fig.  27)  be  a  spherical  surface  separating  the  two  media 
JJ/j  and  Mr      Let  Khz  the  centre  of  curvature.     AB  is  the  optical 


Fig.  27. 

axis  of  the  system,  F2  the  second,  andi^  the  first,  focal  point.  To 
find  the  image  of  the  luminous  point  Ox,  draw  the  directing  ray 
OxK.  Also  draw  a  ray  from  Ox  parallel  to  the  optic  axis ;  this 
cuts  the  surface  at  hv  and  from  /il  passes  through  F2,  and  its  prolon- 
gation cuts  OxK  zX  bv  which  is  the  image  point.  In  a  similar  way 
the  image  point  b2  of  the  luminous  point  02  is  found.  The  image 
formed  in  this  case  is  real  and  inverted. 


260  HUMAN  PHYSIOLOGY. 

6.  It  can  also  be  seen  from  Fig.  27  that  the  size  of  the  object  is 
to  the  size  of  the  image  as  the  distance  of  the  object  from  the  nodal 
point  K  is  to  the  distance  of  the  image  from  K. 

7.  An  optical  system  may  contain  several  spherical  surfaces  separat- 
ing several  refracting  media.  If  all  the  centres  of  a  spherical  surface 
lie  in  a  straight  line,  the  system  is  called  a  centred  system,  and  the 
straight  line  in  which  all  the  centres  are  located  is  called  the  optical 
axis.  The  refraction  of  such  a  system  can  be  determined  by  find- 
ing the  refraction  of  each  surface  successively  according  to  the  above 
formulae. 

8.  A  svstem  in  which  the  entering  rays  are  converged  is  called  a 
converging  or  collecting  system  [Sammelsystem] .  (Parallel  rays 
are  converged  ;  convergent  rays  are  rendered  more  convergent  ; 
divergent  rays  are  either  rendered  less  divergent,  parallel,  or  con- 
vergent, according  to  the  original  degree  of  divergence. ) 

I.  The  dioptric  system  of  the  normal  resting  eye. — The 
dioptric  system  of  the  eyes  is  a  convergent  system  of  three 
approximately  concentric  spherical  surfaces  placed  between 
four  media.  The  media  are:  air,  aqueous  humor,  lens, 
vitreous  humor.  The  surfaces  of  separation  are  the  anterior 
surface  of  the  cornea  and  the  anterior  and  posterior  surfaces 
of  the  lens.      The  optical  axis  is  called  the  visual  axis  (see 

Fig.  28,  /;y2). 

The  posterior  surface  of  the  cornea  is  disregarded  because  it  is 
parallel  with  the  anterior  surface  and  because  the  index  of  refrac- 
tion of  the  cornea  may  be  regarded  as  the  same  as  that  of  the 
aqueous  humor. 

The  indices  of  refraction  of  the  aqueous  humor  and  of  the 
vitreous  humor  are  1.338,  that  of  the  lens  is  1.455.  The 
radius  of  the  curvature  of  the  corneal  surface  is  8  mm,  of  the 
anterior  surface  of  the  lens  10  mm,  of  the  posterior  surface 
of  the  lens  6  mm.  The  distance  of  the  anterior  surface  of 
the  cornea  from  the  anterior  surface  of  the  lens  is  3.6  mm, 
the  thickness  of  the  lens  is  also  3.6  mm.  The  retina  lies  1  5 
mm  behind  the  posterior  surface  of  the  lens.  From  these 
data  the  dioptric  action  of  the  system  can  be  found. 

The  indices  of  refraction  can  be  determined  only  in  the 
dead  eye,  but  the  radii  and  the  distances  of  the  surfaces  can 
also  be  determined  in  the  living  eye. 

The  lens   is  composed  of  many  layers,   like  an   onion,  and   the 


OPTICS  261 

individual  layers  have  various  indices  of  refraction,  the  index 
increasing  as  we  proceed  to  the  centre.  Because  of  the  order  of 
the  layers,  the  actual  total  index  of  refraction  is  somewhat  larger 
than  the  index  of  the  central  layer. 

The  radii  of  curvature  are  determined  from  the  size  of  the 
reflected  image  of  a  known  object  which  is  formed,  by  reflection,  at 
the  surface.  To  measure  the  size  of  these  images  accurately  the 
ophthalmometer  invented  by  Helmholtz  is  used. 

It  has  been  found  by  calculation  that  the  dioptric  effect  of 
the  eye  can  also  be  produced  by  a  simple  system,  in  which 
the  lens  is  not  present  and  is  replaced  by  vitreous  humor, 
and  in  which  the  reduction  of  refraction,  due  to  omission  of 
the  lens,  is  corrected  by  giving  the  only  remaining  refractive 
surface  (the  surface  of  the  cornea)  a  stronger  curvature  and 
a  different  position.  The  system  is  therefore  reduced  to  a 
single  spherical  surface  placed  between  two  media  (for  the 
aqueous  and  vitreous  humor  have  the  same  index  of  refrac- 
tion). The  radius  of  this  surface  is  5.017  mm;  the  distance 
of  the  centre  of  curvature  (nodal  point)  from  the  anterior 
surface  of  the  cornea  in  the  real  (not  reduced)  eye  is  7.16 
mm.  The  simplified  system  is  called  the  reduced  or  sche- 
matic eye,  and  by  its  aid  we  can  construct  the  refracted  ray 
of  light  as  indicated  in  Fig.  27.  In  Fig.  28  //is  the  position 
of  the  surface  of  separation  of  the  reduced  eye. 

Strictly  speaking  the  system  of  the  eye  has  two  nodal  points 
(A'j  and  K2,  Fig.  28,  which  lie  6.96  and  7.37  mm  behind  the  vertex 
of  the  cornea),  but  these  lie  so  closely  together  that  thev  may  be 
regarded  as  one.  The  two  nodal  points  have  the  following  char- 
acteristic. A  ray  which,  previous  to  refraction,  passes  in  the  direc- 
tion of  the  first  nodal  point,  passes,  after  refraction,  through  the 
second  nodal  point  and  parallel  to  its  original  course.  Correspond- 
ing to  the  two  nodal  points  there  are  also  two  spherical  surfaces. 
The  points  where  the  optical  axis  cuts  these  two  surfaces  are  called 
the  chief  .points  (hx  and  h.,,  Fig.  28).  The  first  chief  point  lies 
1.94  mm  and  the  second  2.36  mm  behind  the  anterior  surface  of 
the  cornea.  Planes  erected  perpendicular  to  the  optic  axis  at  the 
chief  points  are  called  chief  planes.  The  chief  planes  must  be 
regarded  as  conjugated  planes  of  such  a  nature  that  an  object  which, 
previous  to  refraction,  is  supposed  to  be  located  in  the  first  chief 
plane,  must  have,  after  refraction,  an  image  of  the  same  size  in  the 
second  plane. 


262 


HUMAN   PHYSIOLOGY 


The  nodal,  chief,  and  focal  points  of  the  eye  are  collectively 
called  the  cardinal  points  (cf.  infra). 

The  second  focal  point  of  the  eye  lies  22.23  mm  beind  the 
vertex  of  the  cornea,  the  first  focal  point  12.92  mm  (_/,  and 
fx.  Fig.  28).      The  second  focal  plane  nearly  coincides  with 


'  !/' 

G  \V 

/• 

/      hy 

'aj 

&, 

1*2 

/, 

/ 

G- 

\  J 

/; 

Fig.   28. — Cardinal  Points  of  the  Eye  (see  text). 
GG'  is  the  visual  axis. 

the  retina.  Images  of  infinitely  removed  objects  having 
parallel  rays  fall  on  the  retina.  Hence  the  norma!  retina  can 
clearly  sec  objects  at  an  infinite  distance. 

II.  Accommodation. — The  image  of  a  near  luminous  point 
falls  behind  the  retina  of  the  resting  eye  and  no  image  is 
formed  on  the  retina.  In  its  place  a  luminous  circle 
appears,  the  circle  of  diffusion,  because  the  rays  have  not 
yet  united.  As  the  circles  of  diffusion  of  a  near  luminous 
point  overlap  each  other  the  image  of  a  near  object  on  the 
retina  is  not  sharply  defined,  hence  the  resting  eye  cannot 
clearly  see  near  objects. 

In  order  to  form  upon  the  retina  a  sharply  defined  image 
of  a  near  object,  the  refractive  power  of  the  eye  is  increased 
by  increasing  the  curvature  of  the  surfaces  of  the  lens.  This 
process  is  called  accommodation. 


OPTICS  263 

In  the  condition  of  strong  accommodation  the  radius  of  the 
anterior  surface  of  the  lens  is  6  mm,  of  the  posterior  surface 
5.5  mm;  the  anterior  surface  is  also  slightly  pressed  forward, 
the  posterior  surface  remains  in  its  position.  For  this  condi- 
tion also  a  reduced  eye  maybe  constructed,  the  radius  of  the 
spherical  surface  of  separation  being  4.53  mm,  its  centre  of 
curvature  lying  6.79  mm  behind  the  vertex  of  the  cornea. 
In  this  condition  sharp  images  of  objects  120  mm  distant 
from  the  vertex  of  the  cornea  are  formed  upon  the  retina. 

Purkinje-Sanson  images. — The  change  in  the  curvature 
of  the  lens  shows  itself  by  changes  in  the  size  and  position 
of  the  image  reflected  from  the  surfaces.  If  a  candle  is  held 
on  one  side  of  the  eye,  three  reflected  images  may  be  seen 
if  the  eye  is  looked  at  from  the  other  side  (Fig.  29,  F). 
The  first  image,  formed  by  the  cornea,  is  upright  and  clear; 
the  second,  formed  by  the  anterior  surface  of  the  lens,  lies 
near  and  a  little  behind  the  first;  the  third,  formed  by  the 
posterior  surface  of  the  lens,  is  small  and  inverted.  If  the 
F  jv 


Fig.  29. 

eye  is  accommodated  for  near  vision,  b  and  c  become  smaller 
and  b  approaches  a  (Fig.  29,  N~) ;  this  is  accomplished  by 
the  stronger  curvature  of  the  surfaces  of  the  lens. 

Schemer's  experiment. — In  a  cardboard  make  two  pin-holes 
near  each  other.  Place  the  holes  near  one  eye  and,  the  other  eye 
being  closed,  look  in  the  direction  of  a  near  point.  If  now  the 
experimenter  look  past  the  point  into  the  distance,  the  first  point 
is  seen  double  ;  if  the  near  point  is  looked  at,  only  one  point  is 
seen.  Of  the  rays  emanating  from  the  near  point  two  thin  bundles 
pass  through  the  pin-holes  into  the  eye,  which,  when  the  eye  is 
accommodated,  unite  to  form  one  image  point  on  the  retina  ;  but 


264 


HUMAN  PHYSIOLOGY 


if  the  eye  is  not  accommodated,  they  illuminate  two  different  points 
of  the  retina  because  its  two  rays  of  light  unite  back  of  the  retina. 

Mechanism  of  accommodation  (see  Fig.  30). — The  lens 
L  lies  inclosed  in  the  two  leaves  of  the  capsule  of  the  lens. 
The   capsule   of  the   lens  at  its  border  passes   over  into  the 


Fig.  30.-  Changes  in  the  Lens  during  Accommodation. 
(After  Helmholtz.) 

/•',  far  vision;  JV,  near  vision;  m,  musculus  ciliaris;  ::,  ZjZ,  ,  zonule  of  /inn; 
c,  ciliary  process;    L,  lens. 

zonule  of  Zinn,  zz  and  .;,,-,,  a  folded  membrane  whose 
periphery  is  united  with  the  choroid  where  this  passes  over 
into  the  corpus  ciliare  (Y). 

The  intra-ocular  pressure  produced  by  the  transudation 
of  tissue  fluid  from  the  blood  vessels  into  the  inner  part  of 
the  eye  causes  the  coats  of  the  eye  to  be  taut,  and  thereby 
stretches  the  part  at  which  the  zonule  is  inserted  into  the 
choroid.  Hence  the  zonule  and  the  capsule  of  the  lens  are 
stretched  and  the  lens  is  pressed  together  and  flattened  in 
its  anterior-posterior  direction.  This  is  the  condition  of  the 
lens  in  the  resting  eye  f  big.  30,  F). 

The  fibres  of  the  muscle  of  accommodation  ///  (tensor  of 
the  choroid  or  ciliary  muscles)  in  the  ciliary  body  pass  from 
the  insertion  point  of  the  zonule  to  the  place  where  the 
choroid  has  grown  together  with  the  boundary  between  the 
cornea  and  the  sclerotic.  By  the  contraction  of  these 
muscles  the  part  at  which  the  zonule  is  inserted  is  pulled 
slightly  forward  and  inward  (toward  the  axis  of  the  eye)  and 


OPTICS  265 

thus  shortened.      This  slackens  the  zonule  and  the  capsule 
of  the   lens,   and   the   lens,  in   consequence   of  its  elasticity, 
bulges  forward  so  that  its  curvature  becomes  greater  (Fig 
30,  N). 

The  muscles  of  accommodation  have  smooth  fibres. 

The  oculo-motor  nerve  supplies  them  with  motor  fibres 
which  enter  into  the  ciliary  ganglion  and  thence  proceed,  as 
the  short  ciliary  nerves,  to  the  eye. 

The  accommodation  muscles  of  both  eyes  are  innervated 
simultaneously  and  to  the  same  extent.  Simultaneously  with 
these  the  internal  rectus  and  the  sphincter  iridis  of  both  eyes, 
are  innervated,  so  that  accommodation  is  always  accom- 
panied by  convergence  of  the  eyes  and  contraction  of  the 
pupils. 

Measure  of  accommodation. — The  point  which  the  resting 
eye  sees  clearly  is  called  the  far  point;  the  point  which  the 
most  strongly  accommodated  eye  sees  clearly  is  called  the 
near  point.  The  range  of  accommodation  is  the  distance  of 
the  far  point  from  the  near  point.  .  The  power  of  accommo- 
dation is  measured  by  the  reciprocal  of  the  near  point  minus 
that  of  the  far  point,  hence  for  the  normal  eye,  in  which  the 
near  point  is  o.  12  m, 

ill 

,  or  8. 3  diopters. 


O.  12  00  O.  12 

This  number  expresses  the  refractive  power  which  a  convex 
lens  must  have  in  order  to  have  the  same  dioptric  effect  as 
the  eye  normally  has  during  strongest  accommodation. 
The  power  of  refraction  (diopter)  is  expressed  by  the  recip- 
rocal of  the  focal  length  of  the  lens.  A  lens  having  the 
focal  length  of  1  m  has  the  value  of  1  diopter.  The  power 
of  accommodation  is  therefore  equal  to  that  of  a  lens  of  o.  12 
mm  focal  length.  The  power  of  accommodation  decreases 
with  age,  because  the  lens  becomes  hard  (presbyopia). 

Anomalies  of  refraction  (near-sightedness  or  myopia,  far-sighted- 
ness or  hypermetropia)  are  due  to  abnormal  positions  of  the  retina. 
In  myopia  the  retina  lies  too  far  back,  and  parallel  rays  meet  in. 


266  HUMAN  PHYSIOLOGY 

front  of  the  retina  ;  hence  to  unite  them  on  the  retina,  the  refrac- 
tion of  the  eye  must  be  decreased  by  placing  before  it  a  diverging 
[concave]  lens.  In  hyperrnetropia  the  retina  lies  too  far  forward, 
and  parallel  rays  meet  back  of  the  retina  ;  in  order  that  in  the  rest- 
ing eye  they  may  unite  in  the  retina,  the  power  of  refraction  must 
be  increased,  which  is  accomplished  by  the  converging  [convex] 
lens.  The  normal  eye  is  called  emmetropic;  in  it  the  second 
focal  point  lies  on  the  retina. 

Periscopia  is  the  power  of  the  eye  to  see  clearly  points  lying  far 
aside  from  the  axis  of  the  eye.  The  laws  thus  far  enunciated  apply 
only  to  rays  of  light  which  are  approximately  parallel  with  the  axis  and 
which  meet  the  refracting  surfaces  nearly  at  right  angles.  Rays 
from  luminous  points  lying  far  to  one  side  are  not  accurately  united 
into  an  image  point,  but  are  quite  well  concentrated  at  two  points 
on  two  small  lines,  of  which  the  posterior  one  may  be  regarded  as 
the  analogue  of  an  image  point.  The  real  image  points  of  lateral 
and  infinitely  removed  luminous  points  lie  on  a  curved  surface  which 
approximately  coincides  with  the  curved  surface  of  the  retina. 
This  is  true,  however,  only  for  the  unreduced  eye.  In  the  reduced 
eye  the  curved  surface  does  not  coincide  with  the  retina. 

Imperfection  in  the  dioptric  apparatus. 

i.  Spherical  aberration. — If  a  bundle  of  light  falls  obliquely 
upon  a  spherical  plane  separating  two  media,  the  peripheral  rays 
are  more  refracted  than  the  central  rays,  hence  the  rays  are  not 
accuratelv  united  at  one  point.  This  is  prevented  in  the  eye  by 
the  facts  that  the  surface  of  the  cornea  is  not  perfectly  spherical, 
but  is  more  strongly  curved  in  the  centre  than  at  the  periphery,  and 
that  the  iris  cuts  off  the  peripheral  rays. 

2.  Chromatic  aberration. — The  various  colors  of  the  spectrum 
are  differently  refracted,  the  violet  being  more  strongly  refracted 
than  the  red  ;  hence  the  violet  rays  are  brought  to  a  focus  sooner 
than  the  red  rays.  This  ordinarily  causes  no  disturbance  in  vision, 
but  can  be  observed  by  covering  half  of  the  pupil  of  one  eye  with 
a  piece  of  cardboard  and  gazing  with  this  eye  upon  a  light  object. 
The  borders  of  the  object  appear  colored  because  of  the  chromatic 
aberration. 

3.  Astigmatism. — The  curvature  of  the  surfaces  of  separation 
may  be  unequally  great  in  various  meridians  of  the  surface.  Hence 
the  rays  of  light  from  a  light-bundle  falling  upon  a  given  meridian 
will  be  refracted  differently  from  those  falling  on  another  meridian 
and  will  unite  at  another  place.  Suppose  that  the  meridian  having 
the  greatest  curvature  is  at  right  angles  to  the  meridian  having  the 
least  curvature.  It  will  be  found  that  the  cross-section  of  the 
bundle  of  light  of  parallel  rays  after  refraction  forms  a  straight  line 
at  two  places,  the  first  of  which  has  the  direction  of  the  meridian 


OPTICS  267 

having  the  least  curvature,  and  the  second  the  direction  of  the 
meridian  of  greatest  curvature.  The  normal  eye  is  slightly  astig- 
matic, the  vertical  meridian  having  the  greatest  curvature.  Be- 
cause of  astigmatism,  of  a  number  of  black  lines  all  crossing  at  a 
common  point  only  one  is  clearly  seen;  the  others,  especially  the 
one  at  right  angles  to  that  clearly  seen,  are  less  sharply  defined. 
Severe  astigmatism  causes  disturbances  in  vision  which  may  be 
corrected  by  the  use  of  cylindrical  glasses. 

Entoptical  phenomena. — Opacities  in  the  refracting  media, 
found  in  the  normal  as  well  as  in  the  diseased  eye  (cells  and  fibres 
of  the  vitreous  humor,  accumulation  of  dust  or  flock 'of  mucus  in 
the  cornea,  etc.),  hinder  the  passage  of  light  and  cast  shadows  on 
the  retina  which  are  seen  as  opaque  objects  in  the  luminous  visual 
field.  They  can  be  seen  especially  well  when  a  source  of  light  is 
placed  in  the  first  focal  point  from  which  parallel  rays  pass  through 
the  vitreous  humor.  If  the  eye  is  moved,  the  apparent  position  of 
the  opaque  object  also  moves — muscse  volitantes.  Among  these 
also  belong  the  shadows  cast  by  the  blood  vessels  (see  page  270). 
The  capillary  stream  of  the  retina  can,  under  certain  conditions, 
also  be  seen  entoptically  in  the  form  of  moving  points. 

III.  Function  of  the  iris. — The  iris  has  two  muscles 
(with  smooth  fibres) : 

1.  The  sphincter  of  the  pupil,  a  circular  muscle,  by  the 
contraction  of  which  the  pupil  is  contracted,  is  innervated 
by  the  fibres  of  the  oculo-motor  which  pass  through  the 
ciliary  ganglia  and  the  short  ciliary  nerves. 

2.  The  dilator  of  the  pupil,  radial  fibres  by  the  contrac- 
tion of  which  the  pupil  is  dilated-.  It  is  innervated  by  the 
sympathetic  fibres  which  also  pass  through  the  ciliary 
ganglia. 

The  innervation  of  both  muscles  is  tonic.  Section  of  the 
oculo-motor  causes  dilation  ;  section  of  the  sympathetic,  con- 
traction of  the  pupil. 

The  iris  is  opaque  because  of  its  pigment.      It  serves : 

1 .  As  a  diaphragm  to  cut  off  the  peripheral  rays  and 
thereby  prevent  spherical  aberration  (see  page  266). 

2.  To  regulate  the  amount  of  light  entering  the  eye. 
The  more  light  the  eye  receives  the  more  contracted  the 
pupil.  This  change  in  the  width  of  the  pupil  follows  reflexly 
upon  changes  in  the  amount  of  light  entering  the  eye.      The 


2  68 


HUMAN   PHYSIOLOGY 


centripetal  nerve  of  this  reflex  is  the  optic  nerve.  By  this 
reflex  contraction  of  the  pupil  the  retina  is  saved  from  too 
strong  illumination,  since  the  smaller  the  pupil  the  less  the 
light  that  enters  the  eye. 

Normally  both  pupils  are  of  the  same  size;  the  change  in 
the  pupil  takes  place  in  both  eyes  even  when  the  light 
entering  one  eye  is  changed  (consensual  pupil  reflex).  The 
centres  for  this  reflex  lie  in  the  cervical  cord  (see  page  233). 

The  contraction  of  the  pupil  also  takes  place  during 
accommodation  and  convergence  of  both  eyes.  The  centre 
for  this  process  is  situated  in  the  corpora  quadrigemina  (see 
page  242). 

The  pupil  is  (i)  contracted  by  sleep  and  by  poisons 
(physostigmin) ;  (2)  dilated  by  stimulation  of  many  sensory 
nerves,  muscular  exercise,  dyspnoea,  poisons  (atropin). 

IV .  Ophthalmoscope. — Only  light  falling  upon  the  most 
anterior  part  of  the  eyeball  enters  the  eye.  Light  falling 
upon  the  side  does  not  enter  the  eye  because  of  the  opacity 

J3 


Fig.  31. 

of  the  choroid  and  iris.  The  light  which  has  entered  the 
eye  is  reflected  by  the  retina  back  to  its  source.  Hence  we 
cannot  see  the  background  of  another  person's  eye  because 
no  light  emanates  from  our  own  eye  by  which  the  observed 
eye  is  illuminated.  But  if  a  mirror,  S,  having  an  aperture 
in  its  centre  (Fig.  31)  is  placed  between  two  eyes,  A  and 
B,  in  such  a  position  that  it  throws  rays  of  light  coming  from 


OPTICS  269 

a,  light  I7,  which  is  placed  at  the  side  of  the  head,  into  the 
eye  B,  a  part  of  the  rays  reflected  by  the  background  of 
the  eye  leave  B  and  pass  through  the  aperture  in  the  mirror 
into  the  eye  A.  The  eye  A  then  sees  the  background  of 
the  illuminated  eye  B.  If  both  eyes  are  emmetropic  and  at 
rest,  the  light  reflected  by  B  passes  out  in  parallel  rays  and 
A  sees  the  back  of  B  erect  and  enlarged.  If  the  light  leaves 
B  in  convergent  rays  (in  case  B  is  accommodated  or  myopic 
— as  represented  in  Fig.  31),  the  image  of  the  retina  can  be 
seen  erect  by  placing  a  concave  lens,  making  the  rays 
parallel  or  divergent,  between  A  and  B.  If  a  convex  lens 
of  sufficient  strength  is  placed  between  B  and  S,  the  reflected 
rays  form,  at  some  point  between  S  and  the  lens,  a  real  and 
inverted  image  of  the  background  of  B  which  can  be 
■observed  by  the  eye  of  the  observer  A  (observation  of  in- 
verted image). 

In  the  albino,  diffused  light  enters  the  eye  through  the  trans- 
parent iris  which  contains  no  pigment ;  this  light  can  illuminate  the 
background  of  the  eye.  If  this  diffused  light  is  prevented  from 
-entering  the  eye,  as  by  placing  a  diaphragm  in  front  of  the  eye,  the 
background  of  such  an  eye  also  appears  dark. 

2.   THE  STIMULATION  OF  THE  RETINA  BY  LIGHT. 
SENSATION  OF  LIGHT 

The  elements  of  the  retina  sensitive  to  light  are  the  cones 
and  rods.  From  them  the  stimulation  passes  through  the 
nervous  portion  of  the  retina  and  through  the  optic  nerve  to 
the  brain. 

The  nerve  structure  of  the  retina  is  found  in  the  connective-tissue- 
supporting  elements  and  is  composed  of  three  neurons  placed  one 
behind  the  other  (see  Fig.  32).      They  are  : 

(1)  Neuro-epithelial  cells,  i.e.  the  cones  (2)  and  rods  (s)  with 
their  nucleated  portion  (cone  and  rod  granules,  0]  and  s^,  which 
are  joined  by  processes  to  the  outer  processes  of  the 

(2)  Bi-polar  cells  (<5).  The  inner  processes  of  the  bi-polar 
cells  join  the  protoplasmic  processes  of  the 

(3)  Ganglionic  cells  (g),  whose  axis-cylinders  form  the  optic 
fibres. 

In  addition  to  these,  still  other  cells  and  centrifugal  nerve  fibres 
Lave  been  found  in  the  retina,  but  their  function  is  not  known. 


HUMAN   PH  YSIOL  OG  Y 


The  mosaic  arrangement  of  rods  and  cones  lies  in  the  external 
layer  of  the  retina  (  viewed  from  the  centre  of  the 
eyeball).  To  arrive  at  them,  light  coming  from 
the  vitreous  humor  must  first  pass  through  all  the 
other  layers  of  the  retina. 

The  outer  layer  of  the  retina  in  the  macula  luiea 
contains  only  cones ;  in  the  other  portions  it  con- 
tains cones  and  rods.  In  the  central  part  of  the 
macula  lutea,  that  is,  in  the  fovea  centra/is,  the  cones. 
have  a  diameter  of  2-2.5  M  '•  at  tne  periphery  6-7 
/.i  ;   the  rods  have  a  diameter  of  about  ijx. 

External  to  the  layer  of  rods  and  cones  there  is  a 
layer  of  epithelial  cells  with  delicate  protoplasmic 
processes  which  reach  down  between  the  rods  and 
cones. 

That  the  cones  and  rods  are  the  retinal  elements 
for  the  perception  of  light  is  proven  by  the  shadows 
which  the  blood  vessels  of  the  retina  cast.  In  a  dark 
iiik  Retinal  room  a  light  is  held  to  the  side  of  the  eye. (at  a,  Fig. 
Neurons.  ^3),  while  the  other  eye  is  closed.      The  light  illu- 

minates the  retina  at  the  point  b,  which  is  found  by  drawing  a  line 
from  a  through  the  nodal  point  A' to  the  retina.  From  b  light,  is 
reflected  by  which  other  parts  of  the  retina  are  illuminated  ;   the 


Fig.  32. — Sche- 
matic Repre- 
sentation of 


Fig.  33. 
cause  of  this  sensation  of  light  thus  produced  we  refer  to  the  exter- 
nal world,  hence  we  see  the  visual  field  dimly  illuminated.     One  of 
the  rays  reflected  from  b  falls  upon  the  retinal  vessel  g,  and  hence 


OPTICS  271 

the  point  c  of  the  retina  will  remain  dark  and  we  see  a  dark  spot 
in  the  visual  field  in  the  direction  cd  ( prolongation  of  a  straight 
line  drawn  from  c  through  the  nodal  point).  The  shadows  cast  by 
the  retinal  vessels  upon  the  retina  are  perceived  as  black  ramifying 
lines  in  the  visual  field.  If  now  the  light  is  moved  from  a  to  a, 
the  apparent  position  moves  from  d  to  6,  as  illustrated  in  the  figure. 
From  the  extent  of  both  movements  the  distance  between  g  and  c 
may  be  calculated,  and  it  has  been  found  that  this  corresponds  to 
the  distance  between  the  vascular  nerve-fibre  layer  and  the  layer  of 
rods  and  cones. 

The  place  where  the  optic  nerve  enters  the  eye  [blind  spot]  is 
not  sensitive  to  light,  because  at  that  place  no  rods  and  cones  are 
present.      This  is  demonstrated  as  follows  : 


Fig.   34. 

Close  the  left  eye,  and  with  the  right  eye  look  at  the  cross  a 
(Fig.  34)  while  the  page  is  held  about  25  cm  from  the  eye.  The 
black  circle  is  then  invisible  because  its  image  falls  upon  the  blind 
spot. 

It  has  been  supposed  that  in  the  sensitive  apparatus  a  substance, 
the  so-called  visual  substance,  is  decomposed,  and  that  this  decom- 
position calls  forth  the  stimulation. 

I.  Objectively  demonstrable  changes  in  the  retina  pro- 
duced by  light. — Changes  in  the  retina  produced  by  light 
have  been  demonstrated,  but  their  relation  to  the  sensation 
of  light  is  not  known. 

1 .  Visual  purple  frhodopsin)  is  a  red  pigment  found  in 
the  external  elongation  of  the  rods.  This  is  bleached  by 
light,  the  color  being  restored  in  the  dark  and  also  in  the 
excised  eye  (in  rabbits  in  one  half-hour,  in  frogs  in  one  to 
two  hours).  The  restoration  proceeds  from  the  pigment 
epithelium.  Visual  purple  cannot  be  the  only  visual  sub- 
stance, for  it  is  not  present  in  the  macula  lutea  of  man,  the 
place  of  direct  vision  (see  page  277). 

The  visual  purple  can  be  extracted  from  a  fresh  retina  by  an 
aqueous  solution  of  bile  salts.      This  must  be  done  in  the  dark  or 


272  HUMAN  PHYSIOLOGY 

by  a  sodium  light,  because  the  extracted  visual  purple  is  bleached 
by  daylight,  not  by  red  or  yellow  light.  The  composition  of  visual 
purple  is  not  known. 

2.  In  the  dark  the  pigment  of  the  epithelial  layer  in  a  frog- 
collects  in  a  cell  bod}",  while,  in  the  light,  it  moves  along 
the  processes  between  the  cones  and  rods. 

The  pigment  is  not  directly  necessary  for  the  perception  of  light, 
for  individuals  in  whom  pigments  are  lacking  (albino)  are  able   to 

sec. 

3.  In  frogs  and  fishes  the  inner  processes  of  the  cones 
become  shorter  and  thicker  in  the  light. 

4.  In  the  illuminated  retina  certain  electrical  phenomena, 
connected  with  the  irritation,  have  been  observed,  but  their 
cause  and  significance  are  not  known. 

II.   Visual  sensation. 

A.  The  intensity  of  visual  sensation. — The  intensity  of 
visual  sensation  is  dependent  upon : 

1.  The  intensity  of  the  stimulus.  The  stronger  the  light 
the  greater  the  intensity  of  the  sensation.  The  sensibility 
for  perceiving  the  difference  in  the  intensity  of  different  lights 
follows  Weber's  law  (page  256). 

2.  The  size  of  the  illuminated  portion  of  the  retina.  A 
small  light  object  may  appear  darker  than  a  larger  but  less 
luminous  object. 

3.  The  duration  of  the  action  of  the  light. 

[a)  The  rise  of  visual  sensation. — A  considerable  length 
of  time,  about  O.  16  second,  elapses  between  the  beginning 
of  the  action  of  the  light  and  the  time  that  the  sensation  of 
light  has  reached  its  greatest  intensity.  Hence  a  bright 
light  acting  for  a  very  short  time  may  appear  darker  than  a 
less  bright  light  acting  for  a  longer  time. 

(/>)  Disappearance  of  the  visual  sensation;  positive  after- 
image.— If  the  light  disappears  suddenly,  the  visual  sensa- 
tion remains  for  a  short  time.  This  is  called  the  positive 
after-image.  Upon  this  depends  the  well-known  phenome- 
non that  if,  in  the  dark,  a  glowing  coal  is  moved  forward  and 
backward,  the   coal  does  not  appear  as  a   luminous  point  at 


OPTICS  273 

each  place  where  it  actually  is,  but  as  a  fiery  stripe  corre- 
sponding to  the  path  it  describes.  In  this  case,  new  points 
of  the  retina  are  stimulated  before  the  sensation  of  the 
previously  stimulated  points  has  entirely  disappeared. 

The  individual  visual  sensations  produced  by  a  series  of 
light  stimulations  rapidly  following  each  other  blend  into 
one  visual  sensation.  Each  individual  stimulation  increases 
and  each  interval  between  the  stimulations  decreases,  to  a 
certain  extent,  the  retinal  stimulation ;  but  if  the  light 
stimuli  follow  each  other  sufficiently  rapidly,  the  variations 
in  the  sensations  are  so  small  that  they  are  no  longer  per- 
ceived. The  intensity  of  the  visual  sensation  in  this  case  is 
as  great  as  that  produced  by  a  correspondingly  feebler  light 
acting  continually  (Talbof  s  laze). 

(c)  Fatigue  of  the  retina.  Negative  after-image  or  suc- 
cessive contrast. — By  long  duration  of  the  light,  the  intensity 
of  the  sensation  is  decreased  because  of  the  fatigue  of  the 
retina.  A  fatigued  retina  is  less  irritable  than  one  not 
fatigued.  If  one  looks  for  some  time  at  a  light  field  placed 
on  a  dark  background  and  then  at  a  uniformly  light  field, 
this  does  not  appear  uniformly  light,  but  upon  it  is  seen  a 
dark  area  corresponding  to  the  light  field  first  looked  at. 
This  phenomenon  is  called  negative  after-image  or  successive 
contrast. 

Adaptation  or  the  adjustment  of  the  retina  to  various  in- 
tensities of  light  depends  upon  fatigue  and  restoration.  If 
one  enters  from  a  light  into  a  dark  room,  nothing  is  clearly 
seen  at  first  because  the  retina  is  fatigued ;  gradually  the 
retina  becomes  more  irritable,  being  rested,  and  one  sees 
much  better  in  the  dark.  If  one  enters  from  a  dark  into  a 
lighted  room,  the  light  at  first  blinds  because  of  the  great 
irritability  of  the  retina,  which  is  gradually  decreased  by 
fatigue. 

4.  The  illumination  of  the  surroundings  of  the  observed 
object. — A  light  upon  a  dark  background  appears  lighter 
than  upon  a  bright  background  (simultaneous  contrast). 
This  contrast  is  greatest  at  the  limit  between  the  liedit  and 


2- A  HUMAN  PHYSIOLOGY 

the  dark,  e.g.  a  white  object  on  a  dark  background  appears 
to  be  surrounded  by  a  very  dark  border. 

Irradiation. — Light  objects  upon  a  dark  background  appear 
larger  than  they  really  are.  This  is  due  either  to  the  fact  that  the 
stimulation  of  a  portion  of  the  retina  radiates  to  the  neighboring 
parts  or  that,  because  of  imperfect  accommodation,  the  image  of 
the  light  object  is  enlarged  by  circles  of  diffusion. 

B.  Quality  of  the  visual  sensation. — The  retina  is  stim- 
ulated only  by  rays  whose  wave  lengths  lie  between  0.69^ 
and  0.39^.      These  visible  rays  are  found  in  daylight. 

Strictly  speaking,  not  all  the  visible  rays  are  present  in  daylight, 
for  those  corresponding  to  the  Fraunhofer  lines  are  not  present. 

The  sensation  produced  by  daylight  is  white.  A  white 
color  of  lower  intensity  is  called  gray.  Objects  which  send 
out  no  rays  capable  of  stimulating  the  retina  appear  black. 

The  visible  rays  are  the  more  refractive  the  shorter  their 
■wave  length.  When  the  various  rays  are  separated  by  pass- 
ing the  light  through  a  prism,  it  is  observed  that  they  pro- 
duce various  visual  sensations,  called  color  sensations. 

The  sensation  of 

Red  is  produced  by  rays  of  0.69  u  wave-length. 

Orange        "  "  "  "  0.64" 

Yellow        "  "  "  "0.59" 

Green         "  "  "  "  0.53" 

Blue  "  "  "  "  0.46 "  " 

Violet         "  "  ';  "  0.39  "  " 

The  sensations  of  color  are  produced  by  the  simple  or 
homogeneous  rays  only  in  medium  intensity.  All  rays  which 
in  medium  intensity  appear  colored  are  colorless  in  very 
strong  or  weak  intensity.  If  the  intensity  of  homogeneous 
rays  is  decreased,  the  relative  brightness  is  changed.  The 
spectral  red  is  brighter  in  medium  intensity  and  darker  in 
lesser  intensity  than  the  blue.  This,  however,  can  be 
observed  only  by  the  eye  adapted  to  dim  vision. 

Mixed  colors  are  produced  by  the  simultaneous  action  of 
rays  of  various  wave  lengths  upon  the  retina.  Of  the  mixed 
colors  one,  i.e.  purple,  is  not  found  in  the  spectrum.  It 
is   produced  by  mixing   red  and  violet.       The    mixed    colors 


OPTICS  275 

appear  whiter,  less  saturated,  than  the  corresponding'  spec- 
tral colors.  For  example,  spectral  red  and  yellow  mixed 
form  an  orange  color  which  appears  whiter  than  the  orange 
of  the  spectrum. 

Complementary  colors  are  two  colors  which  by  mixing- 
give  the  sensation  of  white.  The  following  are  pairs  of 
complementary  colors :  red  and  greenish  blue,  orange  and 
blue,  green  and  indigo  blue,  greenish  yellow  and  violet. 

The  theories  of  color  reduce  the  many  color  sensations  to  the 
simultaneous  but  unequal  stimulation  of  a  few  primary  colors.  The 
Young-Helnholtz  theory  assumes  three  primary  color  sensations — 
red,  green,  and  blue,  which  by  the  action  of  a  light  are  always 
stimulated  simultaneously  but  unequally  by  the  individual  homo- 
geneous rays.  By  the  mixing  of  the  various  primary  colors,  the 
different  color  sensations  are  produced.  If  the  three  color  sensa- 
tions are  equally  stimulated,  the  sensation  of  white  is  produced. 

Recently  the  idea  has  been  advanced  that  only  the  cones  of  the 
retina  are  the  apparatus  for  the  color  sensations,  and  that  with 
these  are  connected  three  classes  of  nerves  corresponding  to  the 
three  primary  color  sensations.  The  rods  are  supposed  to  be  sen- 
sitive only  to  white  light  of  low  intensity,  and  this  sensation  is 
brought  about  by  the  decomposition  of  the  visual  purple.  Accord- 
ing to  this  view,  only  the  rods  are  stimulated  by  light  of  very  low 
intensity,  which  therefore  appears  colorless,  while  such  light  is  not 
able  to  stimulate  the  cones.  In  dim  light  we  therefore  see  chieflv 
with  the  rods,  in  bright  light  with  the  cones. 

Hering's  theory  of  opposite  colors  assumes  six  primary  color- 
sensations,  which  are  classified  into  three  groups  of  two  sensations 
each: 

1.  White  and  black  :  2.  Red  and  green  ;  3.  Blue  and  yellow. 
For  each  group  a  visual  substance  is  assumed  by  whose  changes 
sensations  are  produced.  The  changes  of  the  substance  may  be  of 
two  kinds  ;  the  one  kind  produces  one  sensation,  the  other,  oppo- 
site in  character  to  the  first,  produces  the  other  sensation.  Of  the 
two  opposite  processes,  one  is  supposed  to  be  the  dissimilation,  the 
other  the  assimilation,  of  the  visual  substance. 

The  retina  is  sensitive  to  colors  only  in  its  central  portion. 
As  we  proceed  to  the  periphery  the  power  of  discerning 
colors  decreases.  The  outermost  parts  of  the  retina  are 
color-blind. 

Besides  the  color-blindness  in  the  peripheral  region  of  the  retina, 
pathological  color-blindness  of  the  whole  retina  occurs. 
This  color-blindness  may  be  : 


276  HUMAN   PHYSIOLOGY 

\.  Total,  in  which  all  color  sensations  are  absent,  all  objects 
appearing  colorless. 

2.    Partial. 

Partially  color-blind  persons  have  but  two  kinds  of  color  sensa- 
tions : 

(a)  The  more  general  form,  the  red-green  blindness,  in  which 
only  blue  and  yellow  give  rise  to  sensations,  while  red  and  green 
appear  colorless. 

(//)  The  blue-yellow  blindness,  in  which  only  the  red  and  green 
give  rise  to  sensations,  while  blue  and  yellow  appear  colorless. 

The  red-green  blind  can  be  divided  into  two  groups  which  are 
separated  from  each  other  by  typical  differences  in  the  lack  of 
color  sensations.  For  the  one  red  or  bluish  green  are  colorless, 
for  the  other  purple-red  and  green. 

Color-blindness  has  been  explained  either  by  the  lack  of  certain 
primary  sensations  or  by  changes  in  the  irritability  of  the  elements 
of  color  sensations. 

The  negative  after-image  of  a  color  sensation  has  the 
color  complementary  to  the  original  color.  A  colored  light 
upon  a  colorless  background  calls  forth  a  colored  simul- 
taneous contrast,  in  which  the  background  has  the  color 
complementary  to  that  of  the  colored  light. 

:;.   VISUAL    PERCEPTION 

I.   Monocular  vision. 

Space  sensation  of  the  retina. — We  are  able  to  see 
objects  of  the  outer  world  clearly  in  their  position  because 
we  can  distinguish  different  luminous  object  points.  The 
distinguishing  of  several  object  points  is  rendered  possible 
by  the  mosaic  construction  "of  the  retina  from  elements  each 
of  which  produces  a  separate  sensation  when  it  is  stimulated 
by  light  from  a  luminous  point.  In  the  fovea  centralis  each 
cone  max*  be  regarded  as  such  an  element,  but  at  the 
periphery  of  the  retina  several  of  the  rods  and  cones  collect- 
ively form  one  element. 

From  experience  we  seek  the  source  of  the  light  which 
has  stimulated  a  sensational  clement,  in  the  line  drawn  from 
this  element  through  the  nodal  point  outward  (see  pages 
258  and  261).  Hence  by  vision  with  one  eye  we  are  able  to 
tell  the  direction  in  which  the  object  lies. 


OPTICS  -  277 

Two  separate  object  points  are  seen  distinctly  when  their 
image  points  fall  upon  two  sensational  elements  separated 
by  at  least  one  other  element. 

Acuteness  of  vision  is  the  power  by  which  two  luminous 
points  can  be  distinctly  seen.  The  acuteness  of  vision  is  the 
greater  the  smaller  the  diameter  of  the  sensational  element 
or  the  smaller  "the  smallest  visual  angle,"  when  the  lumi- 
nous points  can  still  be  seen  as  distinct  points.  The  visual 
angle  is  the  angle  which  the  direction  rays  from  the  luminous 
points  form  with  each  other. 

We  can  discriminate  between  direct  and  indirect  vision. 
A  point  seen  by  direct  vision  is  called  the  fixed  object  point. 
We  see  less  distinctly  by  indirect  than  by  direct  vision. 

The  fovea  centralis  functions  in  direct  vision.  It  has  the 
greatest  acuteness  of  vision,  and  by  means  of  it  we  can,  under 
favorable  circumstances,  distinguish  two  luminous  points 
which  form  a  visual  angle  of  40  seconds.  This  corresponds 
to  a  diameter  of  ^/.i  of  the  sensational  element  (a  little  more 
than  the  diameter  of  a  cone  in  the  fovea).  The  peripheral 
portions  of  the  retina  function  in  indirect  vision  and  have  less 
acuteness  of  vision. 

Oculists  regard  five  minutes  as  normally  the  smallest  visual 
angle  for  the  fovea,  which  is  true  for  the  method  generally  in  vogue 
for  determining  acuteness  of  vision  (reading  of  letter). 

The  direction  ray  drawn  through  the  fovea  is  called  the 
visual  axis  or  line  of  fixation  (see  Fig.  28,  G  G') ;  in  it  lies 
the  luminous  point  which  we  fix  upon  in  seeing.  This  line 
does  not  coincide  with  the  optical  axis,  but  its  anterior  end 
is  a  little  inward  from  the  optical  axis.  The  angle  formed 
by  these  two  lines  is  called  the  "  angle  a  "  and  is  about  J° . 

The  visual  field  is  the  field  in  which  all  the  luminous 
points  seen  by  the  stationary  eye  seem  to  lie.  The  visual 
field  therefore  includes  all  the  directions  in  which  the  station- 
ary eye  can  see  objects.  Its  extent  is  indicated  by  the 
angles  which  the  lines  drawn  from  the  limits  of  the  visual 
field  through  the  nodal  point  form  with  the  visual  axis. 
The   extent  of  the  visual   field  is  outward    70-900,    inward 


278 


HUM. -IN   PHYSIOLOGY 


50-60  ,  upward  45— 550,  downward  65—70°.  The  perimeter 
is  used  in  determining'  the  field. 

II.   Movements  of  the  eyes. 

1.  Movement  of  One  eye. — (a)  General  observations. — 
The  external  eye  muscles  turn  the  eyeball  about  a  point 
lying  on  the  optical  axis,  13.557  mm  behind  the  cornea. 
The  eye  and  its  socket  form  a  ball-and-socket  joint  (see 
page  202). 

The  monocular  field  of  vision  [Blickfeld]  is  the  field  which 
includes  all  the  luminous  points  that  can  be  seen  by  the 
moving  eye,  the  head  being  held  quiet. 

Primary  position  is  the  position  of  the  eye  when  a  person 
looks  straight  forward  into  the  distance,  the  head  being  held 

A. 


Fig.  35. — Muscle  and  Axes  of  Rotation  of  the  Eye.    (After  Helmholtz.) 

a.  rectus  externus;  s,  rectus  superior;  i.  rectus  internus;  t,  obliquus  superior; 
u,  trochlea;  A,  optical  axis;  DD,  axis  of  rotation  of  the  rectus  superior  and 
inferior;  B,  axis  of  rotation  of  the  obliquus  superior  and  inferior;  v.  insertion  of 
obliquus  inferior. 

erect.  In  the  primary  position  the  visual  axis  is  horizontal 
and  parallel  to  the  median  plane  of  the  bod)'.  For  any 
given  position  of  the  visual  line  it  is  mechanically  possible 
that  the  eye  can  still  assume  man}'  positions  because  of  its 


OPTICS  279 

ability  to  turn  around  the  visual  line  as  an  axis.  In  reality 
such  a  turning  does  not  take  place,  but  for  each  position  of 
the  visual  line  the  whole  eye  has  a  definite  position.  This 
is  due  to  the  peculiar  coordination  of  the  innervation  of  the 
eye  muscles.  The  position  of  the  eye  for  any  given  position 
of  the  visual  axis  is  such  as  if  it  moved  from  the  primary  to 
the  new  position  by  rotating  around  an  axis  perpendicular 
to  the  visual  axis  in  the  primary  and  the  new  position. 


obi. inf. 
50,  ' 


r.sup. 


r50t'         40         30       20      1010\       10      20       30         M  rfot 


40 
obi.  sup 


30    d 


40 


r.inf 

Fig.  36. — Action  of  the  Eye  Muscles. 

Lines  described  by  the  line  of  vision  in  the  visual  field  when  the  eyeball  is 
turned  from  its  primary  position  by  some  muscle  of  the  eye.  The  movements  of 
the  point  of  vision  [Blickpunkt]  corresponding  to  the  angle  of  rotation  are  indi- 
cated on  the  lines  in  degrees.  The  distance  of  the  plane  of  the  paper  from  the 
point  of  rotation  of  the  eye  equals  the  line  dd.  The  position  which  the  horizontal 
meridian  in  a  primary  position  assumes  is  indicated  at  the  end  of  each  line. 

(/?)  Action  of  the  individual  muscles  (see  Figs.  35  and  $6). 
■ — The  change  in  position  of  the  eye  may  be  stated  as  fol- 
lows : 

I.    Change  in  the  position   of  the  anterior  surface  of  the 


280  HUMAN  PHYSIOLOGY 

cornea,  i.e.  raising,  lowering',  adduction  (to  nasal  side)  and 
abduction  (to  malar  side). 

2.  Deviation  of  the  perpendicular  meridian  of  the  cornea 
in  the  primary  position  from  the  perpendicular  (wheel  move- 
ment inward  when  the  upper  part  of  the  meridian  is  bent 
toward  the  median  plane ;  wheel  movement  outward  when 
this  part  is  bent  away  from  the  median  plane). 

The  eye  is  turned  from  the  primary  position: 

1.  By  the  rectus  externus ;   abduction. 

2.  By  the  rectus  interims;   adduction. 

3.  By  the  rectus  superior;  upward,  adduction  and  wheel 
movement  inward. 

4.  By  the  rectus  inferior;  downward,  adduction  and 
wheel  movement  outward. 

5.  By  the  obliquus  inferior;  upward,  abduction  and  wheel 
movement  outward. 

6.  By  the  obliquus  superior;  downward,  abduction  and 
wheel  movement  inward. 

The  action  of  these  muscles  is  illustrated  in  Fig.  36. 

(c)  Combined  action  of  the  muscles  of  one  eye. — The  rectus 
superior  and  obliquus  inferior  are  always  simultaneously 
innervated  (from  a  coordination  centre) ;  also  the  rectus 
inferior  and  obliquus  superior. 

The  secondary  position,  i.e.  abduction,  adduction,  raising, 
lowering,  are  not  accompanied  by  wheel  movements.  By 
simple  raising  and  lowering,  the  adduction  and  wheel  move- 
ment produced  by  one  of  the  active  muscles  is  destroyed  by 
the  opposite  action  of  the  other  muscle.  All  other  move- 
ments {tertiary  position)  are  associated  with  wheel  move- 
ments.     This  wheel  movement  takes  place: 

1.  Outward  {p.  inf.)  by  raising  (r.  sup.)  and  abduction 
(r.  e,-t.): 

2.  Inward  ir.  sup.  1  by  raising  {p.  inf.)  and  adduction 
</-.  int.); 

3.  Inward  (p.  sup.)  by  lowering  [r.  inf.)  and  abduction 
(r.  ext.)\ 


OPTICS  28  r 

4.  Outward  (;-.  inf.)  by  lowering  (o.  sup.)  and  adduction 
(;-.  int.). 

2.  Combined  action  of  the  muscles  of  both  eyes. — The 
two  eyes  are  moved  simultaneously.  They  are  innervated 
from  a  common  centre.      The  movements  are  as  follows : 

1 .  Rcct.  sup.  and  oil.  inf.  on  both  sides  =  raising"  of  both 
eyes ; 

2.  Rcct.  inf.  and  obi.  sup.  on  both  sides  ^^  lowering  of 
both  eyes ; 

3.  The  left  rcct.  int.  and  right  rcct.  ext.  =  movement  of 
both  eyes  to  the  right; 

4.  The  left  rcct.  cxt.  and  right  rcct.  int.  =  movement  of 
both  eyes  to  the  left. 

5.  Rcct.  int.  on  both  sides  =  convergence; 

6.  Rcct.  cxt.  on  both  sides  =  divergence. 

With  the  convergence  is  associated  accommodation  and  con- 
striction of  pupil. 

Binocular  point  of  vision  is  the  point  in  space  on  which 
both  eyes  are  fixed  and  in  which,  therefore,  the  two  visual 
axes  meet. 

Binocular  field  of  vision  is  the  field  which  includes  all  the 
object  points  which  can  be  perceived  by  the  two  eyes  when 
the  head  is  held  stationary. 

The  monocular  fields  of  the  two  eyes  nearly  but  not  altogether 
cover  each  other.  But  the  binocular  field  of  vision  is  much  smaller 
than  that  part  of  the  monocular  fields  common  to  both  eyes,  for 
the  two  visual  axes  cannot  be  directed  simultaneously  upon  a  point 
upon  which  each  visual  axis  can  independently  be  directed. 

III.   Binocular  vision. 

1.  Single  vision  with,  both  eyes  [diplopia]. — Those 
objects  in  the  outer  world  whose  images  fall  on  identical 
points  of  both  retinae  are  seen  as  single  objects.  Identical 
points  of  the  two  retinae  are  therefore  such  points  whose 
simultaneous  stimulation  by  a  luminous  object  gives  rise  to 
a  single  sensation. 

A  pair  of  identical  points  are,  for  example,  the  two  foveae 
centralis,  and  also  two  points  on  both  retinae  equidistant  and 


282  HUMAN  PHYSIOLOGY 

located   in  the   same   direction   from  the  foveas  centralis  (see 

Fig.  37)- 

I  r 


Fig.  37. — Identical  Points  on  the  Retin.e. 
The  right  (r)  and  the  left  (/)  retina  are  divided  into  the  quadrants  I,  2,  3,  and 
4  by  the  perpendicular  and  horizontal  lines  drawn  through  the  foveas  c.      If  the 
points  c  and  the  corresponding  dividing  lines  are  placed  over  each  other,  every 
point  of  one  retina  will  be  covered  by  its  identical  point  of  the  other  retina. 

A  luminous  point  whose  image  does  not  fall  on  identical 
points  of  the  retinae  is  seen  double. 

If  identical  points  of  the  retinae  are  stimulated  by  different 
objects,  the  two  objects  are  not  seen  simultaneously,  but  first 
one  and  then  the  other  is  seen,  according  to  whether  the 
attention  is  first  fixed  upon  the  one  or  upon  the  other.  This 
is  called  the  struggle  of  the  two  fields  of  vision  [Wettstreit 
der  Sehfelder]. 

For  a  given  position  of  the  eyes  the  field  in  which  all 
points  are  seen  as  single  points  is  called  the  horopter. 

To  find  the  horopter,  draw  lines  from  a  pair  of  identical  points 
through  the  nodal  points;  the  point  where  these  two  lines  cross  is 
seen  as  a  single  point.  All  the  points  thus  found  form  the  horopter 
for  this  given  position  of  the  eyes. 

2.  Perception  of  solidity. — By  binocular  vision  we  can 
see  an  object  from  two  different  directions.  Hence  the  posi- 
tion of  the  object  is  where  the  two  visual  lines  cut  each 
other.  If  a  solid  object  is  viewed  with  both  eyes,  two  dis- 
tinct images  of  the  object  are  formed  upon  the  retinae  because 
the  two  eyes  view  the  object  from  two  different  points  of 
view.  Hence  the  images  falling  upon  identical  points  of  the 
retinae  are  not  the  same.  Consequently  only  a  part  of  the 
points  of  the  observed  object  appear  as  single  points;  the 
others  are  seen  double.  This  gives  us  the  impression  of  a 
solid  body. 


OPTICS  283 

If  we  present  to  each  eye,  from  its  own  standpoint,  a  pic- 
ture of  the  same  body,  the  eyes  see  the  pictured  object 
as  a  solid  body.  The  instrument  by  which  this  is  done  is 
called  the  stereoscope. 

The  judgment  concerning  the  distance  and  the  direction 
of  an  object  is  based  chiefly  upon  the  degree  of  contraction 
which  the  external  eye  muscles  and  the  muscle  of  accom- 
modation undergo  in  fixing  the  gaze  upon  the  object.  The 
judgment  of  the  size  of  the  object  is  formed  by  comparison 
with  an  object  of  known  size,  correction  being  made  for  the 
distance  of  the  object.  Errors  made  in  judging  the  distance 
and  direction  of  objects  are  called  optical  illusions. 

1 .  The  protective  organs  of  the  eye.  — By  the  closing  of  the 
eyelid  the  eyeball  is  protected  from  injurious  external  influ- 
ences. This  is  accomplished  by  the  orbicularis  palpebrarum, 
which  is  innervated  by  the  facial.  The  closing  may  be  a 
voluntary  or  a  reflex  act.  The  reflex  closing  is  brought 
about  by  too  strong  stimulation  of  the  retina  (blinking)  or 
hy  the  stimulation  of  the  cornea  and  conjunctiva. 

The  surface  of  the  eye  is  kept  moist  and  clean  by  the 
tears.  The  tears  flow  from  the  efferent  duct  of  the  lachry- 
mal gland  into  the  conjunctival  sac  and  are  distributed  by 
the  closing  of  the  lid  and  by  the  movements  of  the  eye.  In 
this  manner  the  closing  of  the  lid  keeps  the  cornea  moist 
and  clean.  From  the  conjunctival  sac  the  tears  flow  through 
the  nasal  duct  into  the  nose. 

The  Meibomian  glands  in  the  eyelids  are  sebaceous  glands 
whose  secretion  oils  the  borders  of  the  lids.  This  prevents 
the  flowing  of  the  tears  over  the  lids. 

2.  Blood  and  lymph  circulation  in  the  eye. — The  blood 
enters  the  eye : 

(1)  By  the  central  artery  of  the  retina,  which  supplies  the 
retina  with  blood. 

(2)  By  the  ciliary  arteries  which  pass  to  the  choroid. 
Communications  exist  between  the  branches  of  the  vessels 

of  the  retina  and  of  the  choroid,  especially  near  the  entrance 
of  the  optic  nerve. 


284  HUMAN  PHYSIOLOGY 

The  blood  leaves  the  eye : 

(1)  By  the  central  vein  of  the  retina  (from  the  retina). 

(2)  By  the  vorticosae  veins  (from  the  choroid  . 

The  aqueous  humor  may  be  regarded  as  lymph  which,  in 
the  posterior  chamber  of  the  eye,  is  secreted  by  the  ciliary 
processes  and  the  posterior  surface  of  the  iris.  The  dis- 
charge of  the  aqueous  humor  takes  place  in  the  anterior 
chamber  in  the  angle  between  the  sclerotic  and  the  iris. 
The  lymph  is  here  absorbed  into  a  venous  vessel,  the  canal 
ofSchlemm  (s,  Fig.  30),  There  are  no  special  lymph  ves- 
sels in  the  eye. 

The  vitreous  humor  is  a  jelly-like  tissue,  consisting  of  an 
alkaline  fluid  inclosed  in  a  delicate  membrane.  This  mem- 
brane is  composed  of  collagen  ;  the  fluid  contains  1 .  y'c  solids, 
including  traces  of  albumin  and  globulin,  also  a  proteid  sub- 
stance called  mucoid,  and  finally  9^  salts.  The  lens  is  com- 
posed of  fibres  which  may  be  regarded  as  cells  ;  these  contain 
about  36^  solids,  chiefly  a  globulin-like  proteid  (3; 


CHAPTER    XXII 


THE   EAR 


The  ear  contains  the  sense  organ  of  hearing  and  the 
oro-an  for  perceiving  the  positions  and  movements  of  the 
head. 

1.    THE    AUDITORY    ORGAN 

The  adequate  stimuli  for  the  auditory  organ  are  the  vibra- 
tions of  solid,  liquid,  or  gaseous  bodies,  called  sound  waves, 
because  by  their  action  upon  the  auditory  organ  the}-  give 
rise  to  the  sensation  of  sound.      These  vibrations  are  usually 


Fig.  38. — Diagrammatic  View  of  the  Organs  of  the  Ear. 
(After  Helmhollz.) 
D,  external  auditory  canal;  cc,  membrana  tympani;  BB,   cavity  of  the  tym- 
panum  with   the  auditory  ossicles;    o,   fenestra   ovalis;    r,   fenestra  rotunda;  A, 
cochlea;  E,  Eustachian  tube. 

carried  to  the  ear  by  air.      But  the  vibrations  can  also  be 
carried  to  the  ear  through  the  bones  of  the  head,  as  when 

285 


;S6 


HUMAN   PHYSIOLOGY 


the  source  of  the  vibrations,  e.g.  a  tuning-fork,  is   brought 
into  contact  with  them. 

i .  Conduction  of  sound  in  the  ear  to  the  sensory  appa- 
ratus (see  Fig.  38). 

(a)  The  propagation  of  sound  in  the  external  ear. — The 
external  auditory  canal  (A  Fig.  38)  serves  as  a  funnel  which 
by  reflection  from  its  wall  gathers  the  sound  vibrations  and 
conducts  them  undiminished  to  the  ear-drum  (cc)  which 
closes  the  bottom  of  the  canal.  The  auricle  or  pinna  of  the 
ear  is  the  rudiment  of  the  elongation  of  this  funnel-like 
passage.  The  membrana  tympani  is  set  in  vibration  by  the 
vibrations  which  have  been  conducted  to  it. 

(b)  The  propagation  of  sound  in  the  middle  ear. —  The 
middle  ear  or  tympanum  (BB,  Fig.  38)  is  a  cavity  in  the 
petrous  bone  and  contains  air.  Its  outer  wall  is  formed  by 
the  drum,  its  inner  wall  by  a  bone  in  which  are  two  aper- 
tures closed  by  membranes,  the  round  and  oval  fenestra,-. 

The  membrana  tympani  is  connected  with  the  fenestra 
ovalis  by  the  auditory  ossicles,  which  convey  the  vibrations 

of  the  ear-drum  to  the  mem- 
brane of  the  fenestra  ovalis. 
The  auditory  ossicles  are  the 
hammer,  anvil,  and  stirrup 
(stapes),  see  Fig.   39. 

The  manubrium  of  the 
hammer,  Mm,  is  united  with 
the  ear-drum,  lying  in  its  upper 
vertical  radius.  From  the  neck 
of  the    hammer    proceed    two 

ligaments  to  the   walls  of  the 

Fin.  -xq.— Auditory  Ossicles.  ,  .   ,         ,,  ,, 

:J     jy     ,  .  „  wj.    tympanum    which     allow  the 

Mm,  manubrium  01  malleus;    Alcp,     J      l 

head,  andJ//,  long  process,  of  the  ham-  hammer    to     move     around     Oil 

mer,  £,  incus,  or anvUA^j+shovu  approximately    horizontal 

and  //,   long,  process  ol   the  anvil;   .\  i  l 

stapes.  sagittal  axis.     The  head  of  the 

hammer,  Mcp,  is  united  to  the  anvil  by  a  joint  which  allows  of 
but  little  movement,  and  this  movement  is  largely  prevented 
when  the  manubrium  is  moved  inward  by  a  coglike  process. 


Mm 


THE  EAR  287 

The  anvil,  Jc,  has  two  processes,  one  behind,  Jb, 
which  is  movably  connected  with  the  posterior  wall  of  the 
tympanic  cavity,  and  a  lower  process,  Jl,  whose  point  is 
connected  by  means  of  a  sesamoid  bone  with  the  stapes 
(stirrup)  -S.  The  base  (foot)  of  the  stirrup  is  united  with  the 
membrane  of  the  fenestra  ovalis  (o,  Fig.  38). 

The  auditory  ossicles  form  a  lever  turning  about  the  axis 
of  the  hammer,  one  of  whose  arms  is  the  manubrium  of  the 
hammer,  while  the  other  arm  extends  from  the  axis  to  the 
point  of  the  lower  process  of  the  anvil  and,  through  the 
stirrup,  is  connected  with  the  membrane  of  the  fenestra 
ovalis.  If  the  drum  vibrates  transversely  to  and  fro,  its 
movements  are  carried  by  the  lever  to  the  membrane  of  the 
fenestra  ovalis. 

The  sound-conducting  apparatus  of  the  middle  ear  is  so 
constructed  that  it  is  evenly  set  in  sympathetic  vibration  by 
sound  vibrations  of  various  lengths.  A  free  and  uniformly 
stretched  membrane  gives  out,  when  it  is  struck,  a  certain 
note  whose  pitch  depends  upon  the  size  and  tension  of  the 
membrane.  Such  a  membrane  is  set  in  especially  strong 
vibration  when  in  its  neighborhood  a  note  having  the  same 
pitch  as  that  produced  by  the  membrane  is  sounded.  The 
drum  of  the  ear  has  no  definite  note  of  its  own  because  of  its 
complicated  structure  (funnel-shaped,  being  pulled  inward 
by  the  manubrium  of  the  hammer).  By  this  its  tension  in 
different  directions  is  not  the  same  and  therefore  it  can  have 
no  definite  note  of  its  own.  It  can  therefore  be  set  into 
sympathetic  vibration  to  the  same  extent  by  many  different 
notes. 

The  sound-conduction  apparatus  of  the  ear  is  provided 
with  a  very  effective  damper,  so  that  no  perceptible  after- 
vibrations  occur  when  the  notes  producing  the  vibrations 
have  ceased. 

The  following  muscles  are  inserted  on  the  auditor}-  ossi- 
cles : 

(1)  Tensor  tympani,  which  lies  in  a  bony  canal  extending 
parallel    with    the    Eustachian    tube.      It    is    united    to    the 


2  88  HUMAN  PHYSIOLOGY 

manubrium  of  the  hammer  by  a  tendon  bending  around  a 
bony  process.  By  its  contraction  the  manubrium  is  bent 
inward  and  thus  stretches  the  drum.  It  is  innervated  by 
the  trigeminus. 

(2)  Stapedius,  whose  tendon  is  attached  posteriorly  to  the 
head  of  the  stapes.      It  is  innervated  by  the  facial. 

The  functions  of  these  muscles  are  not  fully  understood.  They 
probably  exist  for  the  purpose  of  rendering  the  conducting  appa- 
ratus more  fixed  when  a  strong  sound  meets  the  ear  in  order  that 
the  vibrations  may  be  made  weaker  and  thus  prevent  the  auditory 
nerve  from  being  too  strongly  stimulated.  By  means  of  the  tensor 
tympani  the  tension  of  the  membrana  tympani  can  be  accommo- 
dated to  very  high  notes. 

The  Eustachian  tube,  a  narrow- canal  ; /:',  Fig.  38),  passes 
from  the  floor  of  the  tympanic  cavity  forward  and  downward 
and  connects  the  middle  ear  with  the  pharynx.  The  tym- 
panic cavity  and  the  Kustachian  tube  are  covered  with 
mucous  membrane.  The  opening  of  the  Kustachian  tube 
into  the  pharynx  is  generally  closed  by  a  fold  in  the  mucous 
membranes.  During  deglutition  it  is  opened  for  a  brief 
period  by  the  contraction  of  the  tensor  muscle  and  the 
levator  palati  mollis.  By  the  opening  of  the  tube  the  pres- 
sure of  the  external  air  and  the  air  in  the  inner  ear  are 
equalized,  which  is  absolutely  necessary  for  the  normal  con- 
duction of  sound  into  the  middle  ear.  If  the  tube  is  closed 
by  catarrhal  swelling  of  its  mucous  membrane,  disturbances 
in  hearing  result.  The  mucous  membrane  of  the  tube  is 
lined  with  cilia  which  move  the  mucus  toward  the  pharynx. 

(<)  The  conduction  of  sound  in  the  internal  ear. — The 
internal  ear,  or  labyrinth,  is  a  cavity  in  the  petrous  bone  and 
is  filled  with  a  fluid.  In  the  outer  wall  of  the  cavity  are  the 
fenestra-  rotundis  and  ovalis. 

The  anterior  part  of  the  internal  car  is  the  cochlea 
(A,  Fig.  38 J,  a  spirally  wound  canal  of  two  and  one-half 
turns,  divided  into  two  parts  by  a  bony  plate.  As  the  bony 
plate  is  interrupted  in  the  cupola,  the  passages  of  the  canal 
communicate  at  this  place  (helicotrema).  One  of  the 
passages,  the  scala  vestibuli,  opens  at  the  base  of  the  cochlea 


THE  EAR 


289 


into  the  median  part  of  the  labyrinth,  the  vestibule,  which 
is  separated  from  the  middle  ear  by  the  fenestra  ovalis. 
The  other  passage  of  the  cochlea,  the  scala  tympani,  ends, 
at  the  base,  in  the  fenestra  rotundis  (compare  Figs  40  and 
40- 

In  the  labyrinth,  therefore,  the  passage  from  the  fenestra 
ovalis  to  the  fenestra  rotundis  goes  through  the  canals  of  the 
cochlea.  By  the  vibrations  of  the  membranes  of  the  fenestra 
ovalis  the  water  in  the  labyrinth  is  caused  to  vibrate  and 
presumably  that  in  the  cochlea,  because  the  passage  from  the 
fenestra  ovalis   to  the   other   yielding   place  of  the  labyrinth 


Fig.  40. — Cross-section  of  the  Cochlea. 

wall  (the  membrane  of  the  fenestra  rotundis)  passes  through 
the  cochlea.  The  movement  of  the  water  in  the  labyrinth 
is  rendered  possible  by  the  existence  of  this  second  flexible 
part  [membrane  of  the  fenestra  rotundis].  The  partition  in 
the  canal  of  the  cochlea  is  partly  membranous,  and  the 
vibrations  of  the  water  of  the  labyrinth  are  conveyed  to  this 
membrane.  This  membrane  contains  the  sensory  apparatus 
which  is  stimulated  by  the  vibrations. 

2.  The  sound-sensations. 

(a)  The  apparatus  for  the  auditory  sensations  (Fig. 
41). — The  septum  of  the  cochlea  canals  consists  of: 

1 .  The  lamina  spiralis  ossea  (/so),  which  extends  from  the 
axis  of  the  cochlea  (modiolus)  into  the  lumen  of  the  cochlea 
canal. 


290 


HUMAN   PHYSIOLOGY 


2.  The  lamina  spiralis  membranacea  forms  the  continua- 
tion of  the  lamina  ossea  and  extends  to  the  outer  wall  of  the 
cochlea.  It  is  formed  by  the  basal  membrane  (b),  composed 
of  parallel  transverse  fibres,  and  contains  the  apparatus  for 


Fig.  41. — Cross-section  of  one  of  the  Coils  of  the  Cochlea. 

(After  Rauber. ) 

SI',  scala  vestibuli;  ST,  scala  tympani;  CC,  canalis  cochlea;  /so,  lamina 
spiralis  ossea;  /',  membrana  basilans;  from  lis  to  Isp,  lamina  spiralis  mem- 
luanacea;   Co,  organ  of  Corti;  nc,  nerve  bundle;    R,  membrane  of  Reissner. 


auditory  sensations,  i.e.  organs  of  Corti   (Co),  placed   upon 
the  basal  membrane.      Each  organ  of  Corti  consists  of: 

1.  The  pillars  of  Corti  (CC,  Fig.  42),  i.e.  two  pillars  bent 
in  the  form  of  the  letter  S,  resting  on  the  membrana  basi- 
laris.  One  is  called  the  inner,  the  other  the  outer,  pillar, 
and  the  two  unite  at  the  top. 

2.  The  cells  of  Corti  or  hair  cells  (//),  cylindrical  cells 
of  which  one  is  placed  internal  and  three  or  four  external  to 
the  pillars.  At  their  free  surface  they  are  provided  with 
small  hairs  which  project  through  perforations  of  a  support- 
insf  membrane,  the  membrana  reticularis.  Above  this  is 
placed  another  membrane,  the  membrana  tectoria  (Mt), 

The  membrane  of  Reissner  (A\  Fig.  41),  which  proceeds 
obliquely  upward  from  the  lamina  spiralis  ossea  and  unites 
with  the  upper  wall  of  the  cochlear  canal,  separates  the 
canalis  cochlea?  (C  C,  Fig.  41),  in  which  the  organs  of  Corti 
are   placed,  from   the   scala  vestibuli.      The   canalis  cochle;e 


THE   EAR 


291 


ends  in  a  blind  sac  in  the  cupola ;   at  the  base  it  passes  into 
the  inner  chamber  of  the  membranous  labyrinth. 


M.b. 


Fig.  42. — Cross-section  of  the  Lamina  Spiralis  Membranacea. 

Lo,  lamina  spiralis  ossea;  N,  cochlear  nerve;  11  n,  nerve  fibres;  C  C,  pillars  of 
Corti;  Mt,  membrana  tectoria;  i\l/>,  membrana  basilaris;  k,  hair  cells;  Mf,  mem- 
bran  a  reticularis;  d,  Deiter's  cells;  Hd,  habenula  denticulata;  Hp,  habenula 
perforata. 

The  membranous  labyrinth  (see  Fig".  43)  is  a  membranous 
covering  of  the  vestibule  and  the   posterior   part  of  the  laby- 


Fig.  43. — The  Membranous  Labyrinth  (Diagrammatic). 

U,  utriculus  with  the  semicircular  canals;   S,  sacculus;  C,  cochlea;  A~  cupola; 
v,  cul-de-sac  of  the  vestibule;    Cr,  canalis  reuniens;  R,  ductus  endolymphaticus. 

rinth,  the  semicircular  canals  (see  page  294).  In  the  vesti- 
bule the  membranous  labyrinth  is  divided  by  constriction 
into  two  parts,  the  anterior  sacculus  and  the  posterior 
utriclus. 

The  membranous  labyrinth    is   filled  by  the  endolymph, 


292  HUMAN  PHYSIOLOGY 

while  the  space  between  the  membranous  and  the  bony  laby- 
rinth is  filled  with  the  perilymph. 

The  auditory  nerve  divides  into  two  branches : 

1.  The  cochlear  nerve,  the  real  nerve  of  hearing,  enters 
at  the  axis  of  the  cochlea  and  in  the  lamina  spiralis  ossea 
spreads  out  its  fibres  like  a  fan.  Its  fibres  finally  unite  with 
the  hair  cells  of  the  organ  of  Corti  (see  Fig.  42,  N,  u  u). 

2.  The  vestibular  nerve  (see  page  295). 

(b)  The  auditory  sensation. — The  membrana  basilaris  is 
set  in  vibration  by  the  perilymph.  By  this  the  cells  of  Corti 
are  probably  mechanically  stimulated  and  thus  the  auditory 
sensation  is  produced. 

Auditory  sensations  may  be  classified  as  tones  and  noises. 
The  tones  (musical)  are  produced  by  regular  vibrations  and 
may  be  distinguished  by  pitch  and  timbre.  The  pitch  of  a 
musical  tone  depends  upon  its  number  of  vibrations.  The 
greater  the  number  of  vibrations  per  second  the  higher  the 
pitch.  The  audible  tones  lie  between  those  having  19  and 
40,000  vibrations  per  second  (11^-  octaves).  The  tones  used 
in  music  lie  between  those  having  33  (contra  C)  and  4000 
(a"")  vibrations. 

The  time  which  the  tone  must  act  in  order  to  be  heard 
depends  upon  the  pitch  of  the  tone.  Those  of  higher  pitch 
need  less  time  than  the  lower  tones.  In  order  to  judge  of 
the  pitch  of  a  tone,  at  least  16  single  vibrations  must  strike 
the  ear.  If  less  than  1 6  vibrations  strike  the  ear.  we  cannot 
accurately  judge  of  the  pitch.  Auditory  sensations,  how- 
ever, are  still  produced  if  but  two  single  vibrations  reach  the 
ear. 

The  accuracy  of  determining  the  pitch  of  a  tone  varies 
much  in  different  individuals.  It  depends  upon  ability  and 
practice.  Trained  musicians  can  still  discriminate  between 
the  pitch  of  two  tones  having  1000  and  1001  vibrations 
(musicians  call  this  Tis  of  a  whole  note). 

The  perception  of  tones  of  different  pitch  has  been  explained  by 
Helmholtz  by  the  resonance  theory  as  follows : 

The  membrana  basilaris  decreases  in  width  as  we  proceed  from 


THE  EAR 


293 


the  cupola  to  the   base    of  the   cochlea    (see  Fig.  44).       As  the 
membrane  is  composed  of  transverse  fibres,  ^        ,  , 

its  tension  in  this  direction  is  greater  than  aV" 
that  in  the  longitudinal  direction,  and  there- 
fore as  a  resonator  it  acts  like  the  strings  of 
a  piano.  If  one  sings  a  certain  note  near 
an  open  piano,  the  string  which  has  the 
same  number  of  vibrations  as  the  note  sung 
is  set  into  sympathetic  vibration,  the  other 
strings  remaining  quiet.  In  the  same  man- 
ner if  a  note  strikes  the  membrana  basilaris, 
that  segment  of  the  membrane  whose  num- 
ber of  vibrations  correspond  to  that  of  the 
note  will  be  made  to  vibrate.  Each  segment 
which  can  vibrate  by  itself  stimulates  the 
cells  of  Corti  found  on  it,  and  therefore 
only    certain  fibres    of   the   auditory   nerve  FlG  _Dia.gr v 

are  stimulated.     The  corresponding  cerebral      the  Membrana  Basi- 
cells,  because  of  their  specific  energy,   per- 
ceive tones  of  certain  pitch. 

The  quality  or  timbre  of  tones. 
Most  tones  are  not  simple  tones  but  are 
accompanied  by  overtones  which,  as  a 
rule,  are  higher  than  the  fundamental  tone.  Each  tone,  in 
a  mixture  of  tones,  gives  rise  to  a  sensation,  hence  several 
sensations  are  produced  which  we  call  the  quality,  or  timbre. 
The  timbre  of  one  and  the  same  fundamental  tone  varies 
with  the  number  and  strength  of  the  accompanying  over- 
tones. 

If  two  tones  whose  number  of  vibrations  have  a  simple 
ratio  (1:2,  2:3,  3:4,  4:5;  are  sounded  simultaneously, 
the  resulting  sound  is  agreeable— consonance.  The  simul- 
taneous sounding  of  two  tones  whose  number  of  vibrations 
are  not  in  a  simple  ratio  produces  a  disagreeable  sound — dis- 
sonance. 

Frequently  we  are  able  to  analyze  a  mixed  sound  into  its 
components ;  we  are  able,  for  example,  to  distinguish  the 
parts  played  by  the  different  instruments  of  an  orchestra. 

If  two  tones  differing  but  little  in  their  number  of  vibra- 
tions are  sounded  simultaneously  in  such  a  way  that  at  one 
time  the  crests  of  both  waves  correspond  and  at  another  the 


LARIS,    UNROLLED. 

a'd' ,  width  of  membrane 
at  the  cupola;  ad,  width 
at  the  base  of  the  coch- 
lea; a'd'  and  ab,  the 
width  of  the  pillars  of 
Corti. 


294  HUMAN  PHYSIOLOGY 

crest  of  one  corresponds  to  the  trough  of  the  other,  beats 
are  heard,  i.e.  periodic  increase  and  decrease  in  the  auditory 
sensation.  Beats  occurring  more  frequently  than  32  per 
second  cause  an  auditory  sensation  called  beat-tone. 

These  beat-tones  are  a  purely  subjective  phenomenon  ;  they  can- 
not, like  other  tones  of  a  mixed  sound,  be  demonstrated  by  the  reso- 
nator, for  they  do  not  affect  the  resonator.  Hence  the  production 
of  auditory  sensations  by  such  tones  cannot  be  explained  by  Helm- 
holtz's  theory  of  resonants. 

The  sensations  of  noises  are  produced  by  irregular  vibra- 
tions in  which  now  one,  now  another  portion  of  the  basilar 
membrane  is  set  in  vibration. 

In  the  sense  of  hearing,  as  in  sight,  there  are  certain 
phenomena  produced  by  the  rise  and  fall  of  the  auditory 
sensation,  as  also  the  phenomenon  of  fatigue. 

Two  sounds  following  each  other  are  still  heard  as  separate 
sounds  if  the  interval  between  them  is  not  less  than  o.  I 
second. 

The  judgment  of  the  direction  and  distance  from  which  a 
sound  comes  is  very  imperfect.  Both  ears  serve  in  judging 
of  the  direction  of  the  sound,  it  coming  from  the  direction 
towards  which  the  ear  most  stimulated  is  turned. 

•1.    THE    SKNSE    ORGANS    FOR    PERCEIVING    THE 
POSITION    AND    MOVEMENTS  OF    THE    HEAD 

The  posterior  part  of  the  bony  labyrinth  is  composed  of 
the  three  semicircular  canals,  which  are  bony  canals  bent  in 
the  form  of  a  C.  The)*  originate  and  end  at  the  vestibule. 
Each  canal  has  at  both  ends  a  dilation  (ampulla).  The 
planes  of  the  superior-anterior  canal  lie  in  the  vertical  longi- 
tudinal plane ;  that  of  the  inferior  posterior  in  the  vertical 
transverse;  that  of  the  lateral  in  the  horizontal  plane. 
Hence  the  three  planes  of  the  semicircular  canals  are  per- 
pendicular to  each  other.  The  bony  canals  surround  the 
membranous  labyrinth  (see  page  291). 

The  thin  walls  of  the  membranous  labyrinth  are  thickened 
in  the  utriculus  and  in  the  sacculus  (maculae  acusticaj  utriculi 
et  sacculi)  and  in  the  ampullae  (crista.*  acusticai). 


THE   EAR  295 

The  epithelial  cells  covering  the  inner  walls  of  the  mem- 
branous labyrinth  form  hair  cells  in  the  macular  and  crista; 
whose  hairs  extend  into  the  cavity  of  the  membranous  laby- 
rinth. These  hair  cells  are  neuro-epithelial  cells  in  which 
the  fibres  of  the  auditory  nerve  end.  A  branch  of  the 
cochlear  nerve  goes  to  the  macula  sacculi,  while  the  vesti- 
bular nerve  goes  to  the  macula  utriculi  and  the  cristae. 

Upon  both  maculae  lies  a  thin  jelly-like  membrane,  the 
membrane  of  the  otoliths  ;  upon  the  surface  of  this  membrane 
lie  the  otoliths  (consisting  of  calcium  carbonate). 

The  fibres  of  the  auditory  nerve  to  this  part  of  the  laby- 
rinth are,  according  to  the  prevalent  theory,  not  nerves  of 
hearing,  but  serve  to  perceive  the  position  and  movements  of 
the  head.  Their  neuro-epithelial  cells  are  supposed  to  be 
mechanically  stimulated  either  by  the  pull  which  the  otoliths 
exert  because  of  their  weight  or  by  the  hydrostatic  pressure 
of  the  endolymph,  which  varies  with  the  different  positions 
of  the  head.  They  may  also  be  stimulated  by  the  move- 
ments of  the  endolymph  brought  about  by  movements  of  the 
head. 

Reflexly  coordinated  movements  for  the  maintenance  of 
the  normal  position  of  the  head  and  the  equilibrium  of  the 
bod}'  are  in  part  called  forth  by  impulses  from  the  semicir- 
cular canals  and  the  otolith  organs.  The  compensator- 
movements  of  the  eye  (page  242)  are  also  called  forth  by 
the  stimulations  from  the  semicircular  canals.  Destruction 
of  the  semicircular  canals  in  animals  is  followed  by  disturb- 
ances in  the  normal  position  and  movements  of  the  head  and 
of  the  whole  body  (forced  positions  and  movements).  It  is 
also  followed  by  diminution  of  the  energy  and  tonus  of 
skeletal  muscles  and  disturbances  in  muscular  sense. 


CHAPTER    XXIII 

SMELL 

THE  organ  of  smell  lies  in  the  regio  olfactoria  of  the  nasal 
mucous    membrane    (upper  part  of  the  septum   nasi,    upper 


-2 


Fig.  45- 
(After  M.  Schultze.) 
A,  epithelium  of  the  mucous  membranes 
of  the  olfactory  region;  a  a,  olfactory  cells; 
/' /',  supporting  cells;  B,  ciliated  epithelial 
cell  from  the  regio  olfactoria. 


-5 


Fig.  46. — Olfactory  Cell  of 
Man.     (After  v.  Brunn.) 

I,  cell-body  with   its  nucleus;   2, 
peripheral    rod,    with     3,    its    ex 
tremity,  furnished  with  hairs,  4;  5, 
central   filament  (beginning    of  an 
olfactory  fibre). 


meatus,  upper  part  of  the  middle  meatus).  It  is  composed 
of  rods  which  lie  between  the  epithelial  cells.  These  rods 
end  externally  in  delicate  hairs  (Figs.  45  and  46) ;  internally 

296 


SMELL  297 

they  are  connected  with  the  olfactory  cells  whose  axis 
cylinders  pass  through  the  cribriform  plate  to  the  bulbus 
olfactorius  (see  page  250). 

Adequate  stimuli  for  the  organ  of  smell  are  gases  carried 
through  the  nose  by  inspiration  and  diffused  in  the  regio 
olfactoria. 

The  liminal  intensity  of  many  substances  is  very  small ;. 
I  millionth  of  I  milligram  of  musk  or  butyric  acid  in  I  litre 
of  air  can  be  detected  by  the  sense  of  smell,  while  of  mer- 
captan  still  less  is  necessary. 

The  organ  of  smell  is  very  soon  fatigued. 

The  sensations  of  smell  have  many  different  qualities 
which  have  not  yet  been  classified.  Mixed  odors  are  pro- 
duced by  the  action  of  two  or  more  odorous  substances. 
Some  odors  are  able  to  neutralize  each  other. 

Corrosive  gases  cause  tactile  sensations  in  the  nasal  mucous, 
membrane  which  may  be  accompanied  by  sensations  of  smell. 


CHAPTER    XXIV 

TASTE 

The  organ  of  taste  is  composed  of  taste  goblets  which  are 
goblet-shaped  structures  with  an  aperture  towards  the  buccal 
cavity  and  contains  spindle-shaped  cells  (see  Figs.  47  and  48). 
The  branches   of  the   nerves  supplying   these  structures  end 


Yig.  47. — Cross-section  of  the  Taste  Papilla  of  the  Tongue,  in  which 
lie  the  Taste-buds. 

between  these  cells.  Taste-goblets  are  found  in  the  epithe- 
lium of  the  circumvallate,  foliate,  and  fungiformes  papilla;  of 
the  tongue,  as  also  in  the  soft  palate  and  the  posterior  pillars 
of  the  fauces.  The  nerve  of  taste  is  the  glossopharyngeal, 
whose  fibres  reach  the  taste  organs  in  part  directly  and  in  part 
through  the  Jacobson's  anastomose  and  lingual  nerve  (see 
page  252). 

Adequate  stimuli  for  the  organs  of  taste  are  liquid  and  dis- 
solved substances,  or  at  least  such  as  are  soluble  in  saliva. 

The  intensity  of  the  taste  sensation  depends  upon  the 
concentration  of  the  solution.  The  liminal  intensity  is 
different  for  the  various  tastable  substances.  The  concen- 
tration necessary  for  some  substances  is  seen  in  the  following 

table: 

29S 


TASTE 


299 


Aloe 1   :  900,000 

Sulphuric  acid I  :  100,000 

Sodium  chloride 1   :  426 

Cane-sugar 1  :  100 

The  intensity  of  taste  sensation  is  greater  the  greater  the 
surface  of  mucous  membrane  affected.  The  taste  sensation 
is  favored  by  pressing  the  tongue  against  the  palate. 


Fig.  48. — Taste-buds  highly  magnified. 
The    best    temperatures    for    taste    lie    between    io°   and 

Hot  or  cold  water  temporarily  inhibits  taste. 
There  are  four  qualities  of  taste  sensations : 

1.  Sweet,  caused  by  sugar,  saccharin,  and  certain  alco- 
hols. 

2.  Bitter,  caused  by  alkaloids. 

3.  Salt,  caused  by  neutral  salts. 

4.  Sour,  caused  by  acids. 

A  solution  tastes  the  more  sour  the  greater  the  number  of  hy- 
drogen atoms  replaceable  by  metals  contained  in  the  unit  of  volume. 

Many  authors  consider  the  alkaline  and  metallic  taste  as  the  fifth 
and  sixth  qualities  of  taste  sensation. 

There  are  also  mixed  taste  sensations  of  two  or  more 
taste  qualities. 

The  sensations  of  taste  are  often  accompanied  by  tactile 
sensations  (astringent  taste)  and  by  sensations  of  smell 
(bouquet  of  wines). 


CHAPTER    XXV 

CUTANE<  >US    SENSATIONS 

The  sense  organs  here  dealt  with  are  chiefly  located  in  the  outer 
skin,  but  are  also  found  in  souk-  parts  of  the  mucous  membranes 
bordering  on  the  skin,  for  example  that  of  the  jaws,  mouth,  nose, 
conjunctiva,  anus,  vagina,  and  urethra.  One  kind  of  these  sense 
organs  is  present  not  only  in  the  skin  and  mucous  membrane,  but 
in  all  organs  of  the  body — the  sense  organs  of  pain. 

i.  The  organs  of  the  tactile  sensation. — The  cutaneous 
sense  organs  are  composed  of  the  endings  of  sensory  nerves 
in  the  skin.      These  endings  may  be  classified  as  follows: 

1.  Free  nerve  endings  between  the  epithelial  cells. 

2.  The  nerve-wreath  of  hairs  which  surround  the  hair- 
bulb  just  beneath  the  opening  of  the  sebaceous  glands. 

3.  Tactile  ee/Is  are  found  in  the  deepest  layers  of  the 
epidermis  and  the  neighboring  layers  of  the  cutis  vera  in 
which  are  found  non-medullated  nerve  fibres. 

4.  End-bulbs.  These  are  spherical  or  oval  bodies  com- 
posed of  a  connective-tissue  capsule  and  a  granular  jelly-like 
medulla — in  which  the  nerve  fibres  end.  In  this  class 
belong  ■ 

(a)  The  taetile  corpuscles  of  Meissner,  elliptical,  trans- 
versely striated  structures.  The  nerve  endings  in  these 
corpuscles  form  a  complicated  network. 

(6)  The  end-bulbs  of  Krause,  cylindrical  structures  in 
which  the  axis  cylinders  are  straight  and  end  free. 

in  The  genital  corpuscles,  oval,  unstriated  bodies  much 
similar  to  the  tactile  corpuscles. 

300 


CUTANEOUS   SENSATIONS.  301 

(d)  The  Vater-Pacini  corpuscles,  whose  capsule  is  com- 
posed of  man\r  concentric  lamellae. 

2.  Qualities  of  cutaneous  sensations. — There  are  four 
■qualities  of  cutaneous  sensations,  viz.,  touch,  heat,  cold,  and 
pain. 

These  various  qualities  are  located  in  various  parts  in  the 
skin.  There  are  portions  whose  stimulation  calls  forth 
tactile  sensations  only,  so-called  tactile  or  touch  points ;  we 
■can  also  discriminate  warmth,  cold,  and  pain  points. 

These  four  kinds  of  points  are  not  evenly  distributed  over  the 
whole  body.  Some  of  them  are  lacking  in  certain  regions  of  the 
body,  e.g.  the  central  part  of  the  cornea  has  only  pain  points,  while 
its  peripheral  portion  is  provided  with  pain  and  cold  points.  The 
glans  penis  contains  no  tactile  points  ;  a  part  of  the  mucous  mem- 
brane of  the  cheek  lacks  pain  points. 

In  those  regions  of  the  body  where  the  four  kinds  of  points  are  all 
found,  the  pain  points  are  generally  most  numerous,  then  follow  the 
tactile  and  cold  points,  while  the  warm  points  are  least  numerous. 

(a)  Tactile  sensation.  —  The  adequate  stimulus  for  the 
tactile  sense  organs  is  the  pressure  exerted  upon  the  skin. 
Concerning  the  nature  of  the  stimulation  of  nerve  endings 
by  pressure  nothing  is  known.  Stimulation  by  pressure 
occurs  only  at  the  boundary  of  the  portion  of  the  skin 
pressed,  where,  therefore,  a  fall  in  pressure  exists. 

For  example,  if  a  finger  is  dipped  in  mercury,  sensations  of 
pressure  are  not  felt  in  the  portion  of  the  finger  below  the  mercury, 
but  at  the  circle  formed  by  the  level  of  the  mercury. 

Tactile  sensations  can  also  be  produced  by  pulling  the  skin.  If 
the  pull  is  exerted  upon  a  very  small  area  of  the  skin,  for  example 
upon  an  individual  tactile  point,  the  sensation  produced  is  nearly 
like  that  produced  by  pressure.  Only  when  a  larger  portion  is 
stimulated  can  Ave  differentiate  between  pull  and  pressure. 

The  organs  for  the  tactile  sensation  are  probably  the  nerve 
wreaths  of  the  hair  [Haarnervenkranze]  and  the  corpuscles 
of  Meissner,  for  the  following  reasons  : 

I.  In  the  regions  of  the  body  covered  with  hair,  a  tactile 
point  is  found  very  near  the  exit  of  each  hair.  The  hair 
serves  as  a  tactile  apparatus,  forming  a  lever  whose  shorter 
arm  is  in  contact  with  the  sensory  mechanism  in  the  skin, 
while  the  longer  arm  receives  the  stimulus. 


302  HUM 'AN  PHYSIOLOGY 

2.  In  those  regions  of  the  body  not  provided  with  hairs, 
the  division  of  the  skin  into  tactile  points  corresponds  with 
the  distribution  of  the  Meissner  corpuscles. 

The  number  of  tactile  points  varies  in  different  parts  of  the 
skin.  In  the  palm  of  the  hand  there  are  from  40  to  50  in 
I  sen  cm. 

The  liminal  intensity  of  the  stimulus  for  the  tactile  sensa- 
tion depends  upon : 

1.  The  place  of  stimulation.  The  lips,  finger-tips,  and 
forehead  are  the  most  sensitive.  For  the  finger-tips  the 
liminal  intensity  is  0.03  g  acting  upon  1  sq.  mm.  surface. 
The  least  sensitive  portions  are  those  covered  with  thick 
epidermis,  for  example  the  soles  of  the  feet.  2.  The  extent 
of  surface  stimulated. 

With  increase  of  surface,  the  liminal  intensity  first  decreases 
rapidly,  then  increases  slowly. 

3.  The  rapidity  of  the  stimulus. 

The  liminal  intensity  is,  to  a  certain  extent,  the  smaller  the 
more  rapidly  the  pressure  is  exerted. 

The  ability  to  distinguish  two  unequal  pressure  stimuli  of 
moderate  intensity  corresponds  with  the  law  of  Weber  (see 
page  256).  The  difference-threshold  is  about  ^  of  the 
already  acting  weight,  i.e.  we  can  recognize  the  difference 
between  two  weights  if  they  have  the  ratio  of  29  :  30. 

The  law  of  ^Yeber  does  not  hold  good  for  very  small  or  very 
large  weights. 

The  tactile  sensations  appear  and  disappear  very  rapidly. 
Even  460  shocks  per  second  are  still  perceived  as  individual 
shocks. 

(b)  and  (V)  The  sensations  of  heat  and  cold. — These 
sensations  are  produced  either  by  increasing  or  decreasing 
the  heat  conveyed  to  the  skin  while  the  loss  of  heat  remains 
constant,  or  by  increasing  or  decreasing  the  loss  of  heat  by 
the  skin  while  the  heat  conveyed  to  it  remains  the  same. 
The  last  is  the  case,  e.g.,  in  applying  warm  or  cold  objects 
to  the  skin.      Sensations  of  temperature  arc  produced  chiefly 


CUTANEOUS  SENSATIONS  303 

by  changes  in  the  temperature  of  the  skin,  to  a  less  extent 

by  constant  high  or  low  temperature. 

Under  certain  circumstances  a  paradoxical  sensation  of  cold  can 
be  produced  by  the  application  of  a  warm  body  to  a  cold  point. 

The  detection  of  differences  in  temperature  is  most  delicate 
when  the  objects  coming  in  contact  with  the  skin  have  a 
temperature  between  270  and  330.  Between  these  tempera- 
tures we  are  able  to  perceive  a  difference  in  temperature  of 
-5L-0  C.  For  the  higher  and  lower  temperatures  the  detec- 
tion of  differences  is  less  accurate. 

The  end-bulbs  of  Krause  are  probably  the  organs  for  the  sensation 
of  cold  ;   the  so-called  genital  corpuscles,  for  sensation  of  heat. 

(d)  Sensation  of  pain. — The  pain  points  can  be  stimu- 
lated by  a  great  number  of  stimuli.  The  intensity  of  pressure 
and  temperature  stimuli  in  order  to  produce  a  sensation  of 
pain  must  be  greater  than  that  necessary  to  produce  sensa- 
tions of  touch  and  temperature. 

The  sense  organs  for  pain  are  probably  the  free  nerve 
endings  in  the  epidermis.  In  the  central  part  of  the  cornea, 
where  only  pain  points  are  present,  only  free  nerve  endings 
are  found. 

The  sensation  of  pain  appears  and  disappears  more 
slowly  than  tactile  and  temperature  sensations.  When  the 
stimulus  is  of  short  duration,  it  can  be  noticed  that  the  sen- 
sation of  pain  is  preceded  by  a  sensation  of  touch  or  tempera- 
ture. When  more  than  20  stimuli  per  second  are  received, 
we  can  no  longer  distinguish  individual  stimuli. 

3.  The  localization  of  sensation  in  the  skin.  Sense  of 
locality. — The  sensations  produced  by  stimulation  of  the 
skin  are  associated  with  conceptions  of  definite  areas  of  the 
skin.      By  this  we  are  able  to  locate  the  place  stimulated. 

The  measure  of  this  power  of  localization  is  the  distance 
that  two  parts  of  the  skin  must  be  separated  in  order  that  by 
their  stimulation  two  distinct  sensations  shall  result.  The 
power  of  localization  has  thus  far  been  determined  chiefly  for 
the  tactile  sensation. 

The  distance  which  these  two  points  must  be  separated 


>°4 


HUM 'AN   PHYSIOLOGY 


depends  on  the  manner  of  stimulation,  that  is,  whether  the 
points  are  stimulated  simultaneously  or  successively.  If 
stimulated  simultaneously,  the  distances  for  various  parts  of 
the  body  are  as  follows: 

Tip  of  tongue i  mm 

Tip  of  finger 2 

Lips 4-5 

Forehead 22 

Back  of  hand 31 

Upper  arm  and  thigh 68 

When  the  points  are  stimulated  successively  the  distances 
are  much  smaller,  being  equal  to  the  distances  which  sep- 
arate the  individual  tactile  points.  For  successive  stimula- 
tion, therefore,  each  tactile  point  has  a  special  space  value. 

An  area  of  the  skin  in  which  two  stimuli  cannot  be  distinctly  felt 
is  called  a  tactile  area.  The  tactile  areas  for  successive  stimulation 
are  smaller  than  those  for  simultaneous  stimulation. 


CHAPTER    XXVI 

ORGAN    SENSATIONS 

THE  organ  sensations  are  produced  by  the  stimulations  of 
sensory  nerves  of  an  organ  by  the  internal  processes  taking 
place  in  that  organ. 

They  may  be  classified  as  follows : 

i .  Sensations  of  pain  may  proceed  from  all  organs  of  the 
body.  The  quality  of  these  sensations  is  the  same  as  that 
of  the  pain  sensations  from  the  skin.  But  the  power  of 
localizing  the  pain  in  the  organ  is  very  imperfect. 

2.  The  sensation  of  muscle  tension.  This  enables  us  to 
estimate  the  weight  of  a  raised  body.  The  muscular  sense 
is  measured  by  determining  the  accuracy  with  which  the 
weight  of  a  raised  body  is  estimated. 

These  sensations  are  produced  by  the  stimulation  of  the 
sensory  nerves  not  only  in  the  muscles,  but  also  in  the 
tendons.  In  fact  the  nerves  of  the  tendons  seem  to  be  of 
greater  importance  for  the  sensations  of  tension  than  those 
of  the  muscles.  But  the  nerves  of  the  muscles  sooner  call 
forth  sensations  of  the  degree  of  muscular  activity  (fatigue 
sensation). 

3.  The  position  of  the  limbs  of  the  body  is  probably  per- 
ceived by  the  sensibility  of  the  joints,  which  may  be  regarded 
as  closely  related  to  the  tactile  sensation  of  the  skin. 

The  sensibility  of  muscles,  tendons,  and  joints  serves  in 
judging  the  position  and  movements  of  the  bod}-. 

Centripetal  fibres  from  the  muscles,  tendons,  and  joints 
also  call  forth  reflexly  coordinated  movements  for  the  main- 
tenance  of  the   equilibrium  of  the  bod)-.      If  the  centripetal 


306  HUM AN  PHYSIOLOGY 

parts   are   diseased,  as  in    locomotor  ataxia  (see   page  229), 
disturbances  in  the  movements  occur. 

It  is  supposed  by  many  authors  that  muscular  sensations 
are  due  to  the  fact  that  we  are  conscious  of  the  degree  of 
innervation  of  the  motor  nerve  in  the  central  organs. 

There  are  still  a  number  of  organ  sensations  which  are  of 
such  an  indefinite  character  that  at  present  little  can,  with 
certainty,  be  said  about  them.  The  knowledge  concerning 
them  is  diminished  by  the  fact  that  the}'  are  often  accom- 
panied by  strong  feelings  (bonheur  and  ennui)  by  which  their 
quality  is  masked.  The}'  are  generally  called  common  sen- 
sations and  include  hunger,  thirst,  itching,  tickling,  shudder- 
ing, fatigue,  pleasure,  ennui,  giddiness,  etc. 

Of  special  physiological  interest  are  the  organ  sensations, 
hunger  and  thirst,  as  they  call  for  the  partaking  of  solid  and 
liquid  food.  The  sensation  of  hunger  is  the  sensation  of  an 
empty  alimentary  canal,  which  disappears  even  when  the 
stomach  is  filled  with  an  undigestible  substance.  In  the 
sensation  of  hunger  the  sensory  nerves  of  the  stomach  and 
intestine  seem  to  play  a  part.  If  the  period  of  hunger  is 
long  continued,  an  undefinable  sensation  of  general  need  of 
food  is  present. 

Thirst  is  the  sensation  produced  by  dryness  of  the  pharynx, 
which  disappears  when   the  mucous  membrane  of  the  palate 
and  the    pharynx    is   moistened.       Hence    the    sensation   of 
thirst  is  produced  by  the   stimulation  of  the  sensory  nerve  of 
the  mucous  membrane  by  drying. 


PART    III 

REPRODUCTION    AND    DEVELOPMENT 


CHAPTER    XXVII 
REPRODUCTION 

The  first  living  beings  must  have  originated  by  spontaneous 
generation  (generatio  tequivoca),  i.e.  the  origination  of  living 
beings  from  lifeless  material.  At  present,  spontaneous  generation, 
so  far  as  we  know,  does  not  occur,  and  new  living  beings  originate 
by  biogenesis,  i.e.  the  formation  of  living  beings  from  separated 
parts  of  previously  existing  living  beings. 

Reproduction  may  be  : 

(a)  Non-sexual  (reproduction  by  fission,  budding,  spore  forma- 
tion). In  this,  one  separated  portion  of  a  living  being  develops  into 
a  new  individual. 

(b)  Sexual  reproduction,  in  which  two  sexually  different  cells 
(egg  and  sperm  cell)  unite  and  develop  into  a  new  living  being. 
These  two  sexual  cells  may  either  originate  from  one  individual  or 
from  two  sexually  different  individuals  (male  and  female). 

Human  beings  are  propagated  by  sexual  reproduction  in 
which  the  egg-cell  provided  by  the  female  unites  with  the 
sperm-cell  furnished  by  the  male  and  from  this  a  new  indi- 
vidual develops. 

1.     THE    MALE     SEX-PRODUCTS    AND    THEIR    FORMA- 
TION 

i .  Composition  of  the  seminal  fluid. — The  seminal  fluid 
is  a  viscid,  whitish,  turbid  fluid  having  a  peculiar  odor  and 
a  neutral  or  alkaline   reaction    in  which   are  suspended   the 

307 


308  HUM  Ah!   PHYSIOLOGY 

solid  elements,  the  spermatozoa.  The  seminal  fluid  contains 
18$  solids  which  include  chiefly  proteids,  as  also  lecithin, 
cholesterin,    fats,    salts,    and    spermin    (Diethylen   diamine). 

Spermin,    having    a    constitution  of  C.,H/ ,.„   /C.,Hr    is  a 

base  and  is  present  in  the  fluid  as  the  salt  of  phosphoric  acid 
and   by  evaporation   of  the  fluid  is   precipitated   as  crystals. 
The     spermatozoa     contain     the    ordinary     constituents     of 
nucleated  cells,  i.e.  proteid.  nucleo-albumin,  nuclein,  nuclein 
bases,  potassium  phosphate. 

The  spermatic  filaments  or  spermatozoa  are  cells  with 
pear-  or  oval-shaped  heads  and  the  attached  rod-shaped 
middle  piece  which  passes  over  into  the  threadlike  tail. 
The  length  of  the  whole  spermatozoon  is  0.05  mm.  The 
cells  are  poor  in  proteids,  the  head  being  the  nucleus,  and 
the  middle  piece  and  the  tail  the  protoplasm. 

The  spermatozoon  moves  about  by  the  whiplike  move- 
ments of  the  tail  and,  during  its  movements,  rotates  about 
its  long  axis.  The  movements  of  the  spermatozoon  are 
most  lively  immediately  after  the  ejection  of  the  seminal 
fluid.  It  is  favored  by  weak  alkali  reaction.  Strong  alkalies 
and  also  acid  reactions  inhibit  the  movements.  In  the 
genital  canals  of  the  female  the  spermatozoa  retain  their 
movements  for  a  very  long  time. 

2.  Formation  of  the  spermatozoa. — The  formation  of  the 
spermatozoa  takes  place  in  the  convoluted  tubules  of  the 
testis.  Certain  cells  of  the  walls  of  these  canals  change  to 
the  spermatoblasts  which  grow  out  into  the  canal.  By  cell 
division  and  the  separation  of  the  newly  built  cells  the 
spermatoblast  forms  the  spermatozoon.  In  this  the  nucleus 
forms  the  head,  while  the  protoplasm  forms  the  middle  piece 
and  tail.  Concerning  details  of  the  morphological  changes 
in  this  process  the  results  of  investigators  are  contradictor}-. 
In  the  testis  there  is  formed  simultaneously,  in  some  unknown 
way,  the  fluid  in  which  the  spermatozoa  are  suspended. 
The  formation  of  spermatozoa  in  the  testis  takes  place,  no 
doubt,  continuously.      The   seminal   fluid  is  passed   into   the 


REPRODUCTION  309 

vasa  deferentia,  where  it  is  stored  up.  During  the  ejacula- 
tion, it  is  mixed  with  the  secretion  of  trie  vesiculae  seminales, 
the  prostate,  and  Cowper's  glands.  Very  little  is  known 
concerning  the  secretions  of  these  glands  or  the  nature  and 
importance  of  their  secretions.  The  prostate  is  supposed  to 
secrete  the  spermin  and  odoriferous  substance  found  in  the 
mixed  seminal  fluid. 

3.  Discharge  of  the  seminal  fluid.  Ejaculation. — The 
discharge  of  the  seminal  fluid  takes  place  during  erection  by 
the  activity  of  certain  muscles  by  which  the  fluid  is  forced 
out  of  the  vasa  deferentia  and  the  urethra. 

(a)  Erection. — During  erection  the  blood  vessels  of  the 
penis  are  well  filled.  This  filling  of  the  penis  is  brought 
about  by 

(1)  Increase  of  blood  carried  to  it  by  the  dilation  of  the 
arteries.  The  dilation  is  produced  by  the  vaso-dilator 
nerves,  the  nervi  erigentes  (see  page  Jj). 

(2)  The  removal  of  the  blood  is  prevented  by  the  com- 
pression of  the  venae  profundae  penis.  The  compression  of 
these  veins  is  produced  by  the  contraction  of  the  museums 
transversus  perinei. 

The  centre  by  which  the  erection  is  brought  about  is  sit- 
uated in  the  lumbar  cord.  It  can  be  stimulated  either 
reflexly  by  the  stimulation  of  the  sensory  nerves  of  the  penis 
or  by  impulses  from  the  cerebral  hemispheres  (psychical). 

{b)  Ejaculation. — The  ejaculation  is  accomplished  by  the 
peristaltic  contractions  of  the  muscles  of  the  vasa  deferentia 
and  vesiculae  seminales  which  drive  the  fluid  into  the  urethra 
and  thence  it  is  propelled  forward  by  the  contraction  of  the 
bulbo-  and  ischio-cavernosus  muscles.  The  passage  of  the 
urinary  bladder  is  cut  off  by  the  erection  of  the  caput 
gallinaginis.  The  act  of  ejaculation  can  be  called  forth 
reflexly  by  stimulating  the  sensory  nerves  of  the  penis. 
The  centre  of  ejaculation  lies  in  the  lumbar  cord. 

The  amount  of  seminal  fluid  discharged  during  one 
ejaculation  is  1-6  cc. 


310  HUMAN  PHYSIOLOGY 

•2.    THE    FEMALE    SEXUAL    PRODUCTS    AND    THEIR 
FORMATION 

i.  The  ovum. — The  female  sexual  cell  or  egg  is  a 
spherical  cell  having  a  diameter  of  o.  I  5-O.2  mm.  Its  proto- 
plasm is  called  egg-yolk;  its  nucleus,  germinal  vesicle.  It 
is  surrounded  by  the  zona  pellucida.  In  the  yolk  we  can 
distinguish  : 

(1)  The  real  living  substance,  the  protoplasm. 

(2)  The  deutoplasm,  or  yolk  granules,  which  serves  as 
food. 

In  the  human  ovum  there  is  but  little  deutoplasm  in  the 
form  of  spheres,  yolk  granules,  lying  in  the  protoplasm.  In 
many  animals,  e.g.  birds,  much  deutoplasm  is  present. 
The  nucleus  of  the  egg  is  generally  spherical,  clear,  and  with 
a  double  contour;  it  surrounds  the  germinal  spot  (macula 
germinativa).  The  zona  pellucida  is  0.02-0.025  mm  thick 
and  radially  striated.  These  striations  are  caused  by  the 
numerous  perforations  of  the  zona  pellucida. 

2.  Formation  of  the  ovum. — The  eggs  in  the  ovary  are 
placed  in  the  Graafian  follicle,  a  spherical  vesicle,  which  in 
mature  condition  has  a  diameter  of  10-15  mm.  The  follicles 
are  imbedded  in  the  connective-tissue  stroma  of  the  ovary 
and  are  surrounded  by  a  vascular  capsule.  The  inner  wall 
of  this  capsule  is  surrounded  by  the  membrana  granulosa  or 
germinativa,  composed  of  many  layers  of  epithelial  cells. 
The  epithelium  forms  at  one  place  a  great  mass  of  cells, 
called  the  discus  proligerus,  in  which  lies  the  ovum.  The 
cavity  of  the  follicle  between  the  discus  proligerus  and  the 
rest  of  the  wall  of  the  follicle  is  filled  with  a  yellowish  fluid 
containing  proteid. 

The  Graafian  follicle  originates  as  follows:  The  surface  of 
the  ovary  is  covered  with  a  cylindrical  epithelium  (the 
so-called  germinal  epithelium)  which  covers  also  the  tubular 
invagination  of  the  surface  of  the  ovary.  These  invagina- 
tions grow  downward  and  are  cut  off  by  the  stroma  of  the 
ovary.  The  separated  tubes  develop  into  the  Graafian 
follicles.      In   the   germinal  epithelium  the  round   egg-cells 


REPRODUCTION  3 1 1 

are  already  present  and  grow  downward  with  the  epithelium 
of  the  tube.  The  first  appearance  of  the  follicle,  that  is,  the 
formation  of  the  primordial  egg,  occurs  in  the  embryo.  At 
first  the  follicles  are  only  0.03  mm  in  diameter.  When  fully 
developed  they  pass  through  the  deep  layers  of  the  stroma 
to  the  surface  of  the  ovary. 

3.  Ovulation  or  discharge  of  the  ovum. — The  discharge 
of  the  egg  takes  place  by  the  bursting  of  the  ripe  Graafian 
follicle.  This  bursting  is  accomplished  by  the  increase  of 
liquid  in  the  follicle  whereby  it  is  enlarged  and  its  walls  are 
rendered  tense  until  they  burst. 

In  the  place  formerly  occupied  by  the  follicle  a  cicatrix  is  formed 
which  is  colored  yellow  by  pigments  :    corpus  luteum. 

The  contents  of  the  follicle,  including  the  egg,  lying 
among  the  cells  of  the  discus  proligerus,  reaches  the  end  of 
the  oviduct,  whose  fimbriated  end  lies  close  to  the  surface  of 
the  ovary.  By  the  ciliated  epithelium  the  egg  is  carried 
through  the  oviduct  to  the  uterus. 

In  human  females  the  discharge  of  the  egg  occurs  regularly 
every  four  weeks.  It  is  accompanied  by  a  capillary  bleeding 
from  the  mucous  membrane  of  the  uterus — menstruation,  last- 
ing from  two  to  three  days.  The  hemorrhage  is  preceded 
by  a  separation  of  the  mucous  membrane  and  the  formation 
of  a  membrane,  the  decidua  menstrualis,  which  is  afterward 
cast  out.      During  menstruation  1 00— 200  g  blood  are  lost. 

4.  The  maturation  of  the  egg.- — Previous  to  fertilization 
certain  changes  take  place  in  the  egg  which  are  collectively 
called  the  maturation  of  the  egg.  The  nucleus  of  the  egg 
moves  towards  the  periphery  and  divides  by  indirect  division 
into  two  nuclei.  One  of  these,  called  the  polar  body,  is  cast 
out  of  the  egg.  The  other  nucleus  again  divides  into  two, 
one  of  which,  the  second  polar  bod}*,  is  also  cast  out.  The 
remaining  nucleus,  called  the  female  pronucleus,  travels  to 
the  centre  of  the  egg. 


31^  HUMAN   PHYSIOLOGY 

3.   FERTILIZATION 

The  spermatozoa  discharged  during  the  act  of  coition  into 
the  vagina  of  the  female  pass  through  the  uterus  and 
oviduct  into  the  upper  part  of  the  oviduct,  called  the  am- 
pulla;. This  is  an  active  movement  and  takes  place  in  the 
direction  opposite  to  that  of  the  movement  of  the  cilia  of  the 
epithelium. 

After  discharge  of  the  egg  fertilization  takes  place,  gen- 
erally in  the  ampulla,  by  the  entrance  of  one  of  the  sperma- 
tozoa into  the  egg.  The  spermatozoon  forces  its  way 
through  the  membrane  of  the  egg  and  proceeds  in  a  radial 
direction  towards  its  centre.  The  tail  of  the  spermatozoon 
becomes  dissolved  in  the  egg,  while  the  head  becomes  the 
male  pronucleus.  The  male  and  female  pronuclei  increase 
in  size  and  approach  each  other.  They  are  now  similar  in 
appearance,  so  that  they  can  no  longer  be  distinguished. 

After  losing  the  nuclear  membrane  the  nuclear  fibres  of 
each  nucleus  break  up  into  a  number  of  loop-shaped  pieces, 
and  these  fragments  are  mixed.  From  the  thus  united  egg 
and  spermatozoon  the  new  individual  develops  by  nucleus- 
and  cell-division  and  cell  differentiation. 

While  the  unfertilized  eggs  are  soon  destroyed,  the  fertil- 
ized egg,  passing  in  about  three  days  through  the  duct  into 
the  uterus,  is  held  in  the  uterus.  It  sinks  between  the  folds 
of  the  mucous  membrane  of  the  uterus,  which  is  greatly 
thickened.  The  walls  of  the  fold  unite  with  the  membrane 
of  the  egg  and  cover  the  egg.  This  part  of  the  mucous 
membrane  subsequently  forms  the  placenta. 


CHAPTER    XXVIII 

PHYSIOLOGY    OF  THE    EMBRYO 

1.    SYNOPSIS    OF    SOME    OF    THE    IMPORTANT    FACTS 
OF    EMBRYONIC    DEVELOPMENT 

By  the  process  of  fertilization  the  fertilized  egg-cell 
divides  into  many  cells  which  form  a  one-cell  layer  below 
the  egg  membrane,  which  takes  no  part  in  this  cell  division. 
By  this  a  cavity  filled  with  fluid,  the  segmentation  cavity,  is 
formed  in  the  centre  of  the  egg.  The  structure  thus  formed 
is  called  a  blastula,  and  the  one-celled  layer  is  called  the 
ectoderm.  The  blastula  expands  by  the  continual  increase 
of  fluid  in  the  segmentation  cavity.  Below  the  ectoderm  a 
second  layer  of  cells,  the  endoderm,  is  formed.  The  manner 
in  which  the  endoderm  is  formed  varies  in  different  animals. 
Finally,  at  a  thickened  portion  of  the  blastula,  a  third  layer, 
the  mesoderm,  is  formed  between  the  ectoderm  and  the 
endoderm.  From  the  ectoderm  originate  the  epithelial  cells 
of  the  skin  and  its  glands,  the  nervous  system,  the  epithelium 
of  the  sense  organs,  and  the  lens.  From  the  endoderm  are 
formed  the  epithelial  cells  of  the  alimentary  canal  and  its 
glands  and  those  of  the  urinary  tubes.  From  the  mesoderm 
originate  the  blood  and  blood  vessels,  the  muscles,  connec- 
tive tissue,  and  the  reproductive  cells. 

The  thickening  of  the  walls  of  the  blastula  at  which  the 
mesoderm  originates  is  called  the  germinal  disk  ;  in  this  the 
first  traces  of  the  embryo  are  seen.  The  germinal  disk 
assumes  a  biscuit  form,  its  borders  curving  inward  and 
thereby  separating   that   part  of  the   cavity  of  the    blastula 


3*4 


HUMAN   PHYSIOLOGY 


Fig.  49. — Development  of  the  Foetal  Membranes  of  a  Mammal. 
(After  Kolliker.) 
1,  ovum  with  zona  pellucida,  blastula,  and  embryonic  area;  2,  formation  of 
yolk-sac  and  amnion;  3,  union  of  the  folds  of  the  amnion,  forming  the  amniotic 
cavity;  formation  of  the  allantois;  4,  decrease  of  the  yolk-sac,  increase  of  the 
allantoic,  formation  of  mouth  and  anus;  5.  reduction  of  the  yolk-sac;  allantois 
joined  to  the  chorion,  enlargement  of  the  amniotic  cavity;  </.  zona  pellucida;  </', 
processes  (villi)  of  zona  sA,  serous  membrane;  sz,  villi;  ch,  chorion,  chz,  chori- 
onic villi;  am,  amnion;  ks,  head-fold  of  amnion;  ah,  amniotic  cavity;  as,  navel- 
cord  with  the  amnion;  <ut\  ectoderm;  i,  endoderm;  mm',  mesoderm;  </</,  embry- 
onic part  of  the  endoderm;  <//",  area  vasculosa;  s(,  sinus  terminalis;  kk,  cavity  of 
the  blastula;  ds,  umbilical  vesicle  (yolk-sac);  '/;',  passage  of  the  umbilical  vesicle; 
al,  allantois;  <■,  embryo;  r,  space  between  chorion  and  amnion;  vl,  ventral  body 
wall;  ////,  pericardial  cavity. 


PHYSIOLOGY   OF   THE  EMBRYO  3l5 

lying  below  the  germinal  disk,  i.e.  the  embryonic  intestine, 
from  the  part  above,  i.e.  the  yolk-sac .  The  connection 
"between  these  two  cavities,  as  long  as  it  is  open,  is  called  the 
Vitelline  duct  (see  Fig.  49). 

The  ectoderm  forms  a  fold  over  the  curved  germinal  disk. 
The  inner  leaf  of  this  fold  grows  over  the  embryo  and  forms, 
by  separating  from  the  blastula,  the  amnion,  which  at  the 
navel  passes  over  into  the  skin  of  the  embryo.  The  outer 
leaf  of  the  fold  joins  the  zona  pellucida  and  forms  with  it  the 
serous  membrane,  which  later  on  is  called  the  chorion.  On 
the  surface  of  the  chorion  villus-like  processes  are  formed 
which  unite  with  the  mucous  membrane  of  the  uterus.  From 
the  posterior  part  of  the  embryonic  intestinal  cavity  a 
tubular  projection,  the  allantois  or  the  urinary  sac,  grows 
out  into  the  space  between  the  yolk-sac  and  the  chorion. 
Its  inner  part  (lying  in  the  embryo)  becomes  the  urinary 
bladder.  The  allantois  grows  outward  until,  in  the  third 
Aveek,  it  joins  the  chorion  and  forms  with  it  the  placenta. 
The  lumen  of  the  allantois  soon  disappears  and  forms  a  cord 
composed  of  mucous  tissue  and  is  called  the  umbilical  cord. 

Chronology  of  the  development  of  the  embryo. 

First  month. 

First  week.  Passage  of  the  egg  through  the  tube ;  fertilization; 
formation  of  the  blastula. 

Second  week.  Blastula  attains  a  diameter  of  5  mm ;  villus-like 
processes  formed  on  the  egg  membrane  ;  first  rudiments  of  embryo  ; 
formation  of  the  spinal  folds  and  of  the  medullary  groove. 

Third  week.  Embryo  about  4  mm  long.  Formation  of  the 
amnion,  yolk-sac,  and  allantois.  The  yolk-sac  circulation  is 
established. 

Fourth  week.  Embryo  from  8  to  n  mm  long.  The  position  of 
the  extremities  is  clearly  visible.  The  three  cerebral  vesicles  are 
present. 

Second  month.  Length  of  embryo  30  mm.  The  yolk-sac  circu- 
lation degenerates,  while  the  placental  circulation  develops.  Forma- 
tion of  the  face  ;  disappearance  of  the  gill-clefts  and  posterior  gill 
arches  ;  the  extremities  become  jointed  ;  first  points  of  ossification  in 
the  hip-bone  and  lower  jaw  ;  abdominal  cavity  closed ;  kidneys 
formed. 

Third  month.  Length  of  embryo  70  mm.  Commencement  of 
sexual  differentiation. 


316  HUMAN  PHYSIOLOGY 

Fourth  month.  Length  of  foetus  17  cm,  weight  100  g.  It  is 
possible  to  distinguish  male  and  female  organs  from  each  other. 
Placenta  weighs  80  g.  First  movements  of  the  extremities.  Meco- 
nium in  intestine. 

Fifth  month.  Length  of  foetus  30  cm,  weight  280  g.  Hair  on. 
the  head  and  body  [lanigo]  appear.  Beginning  of  sebaceous  secre- 
tions.      Placenta  weighs  178  g. 

Sixth  month.  Length  of  fetus  34  cm,  weight  700  g.  The  fat 
layers  of  the  skin  develop.  Movement  of  the  embryo.  Born  dur- 
ing this  month  the  child  makes  feeble  respiratory  movements  but  is 
not  viable. 

Seventh  month.  Length  of  hetus  38  cm,  weight  1300  g.  Born 
during  this  month  the  child  whines  and  is  sometimes  viable. 

Eighth  month.  Length  of  foetus  42  cm,  weight  i57og.  Tes- 
ticles descend.      Child  is  viable. 

Ninth  month.      Length  of  foetus  65  cm,  weight  1970  g. 

The  mature  embryo  is  50  cm  long,  weighs  3  kg. 

2.    METABOLISM   OF  THE  EMBRYO 

{a)  Circulation.  —  In  explaining"  the  embryonic  circulation 
two  periods  must  be  kept  distinct :  (i)  the  period  of  vitel- 
line [yolk-sac]  circulation;  (2)  period  of  the  placental  cir- 
culation. 

(1)  Vitelline  circulation. — The  first  formation  of  vessels 
occurs  near  the  germinal  disk.  From  the  cells  of  the 
mesoderm  originate  the  peripheral  veins  ("sinus  terminalis) 
from  which  spring  the  blood  vessels  of  the  embryo.  From 
the  wall  of  the  vein  solid  cords  of  cells  extend  into  the 
embryo  which  anastomose  and  become  hollow  by  the  forma- 
tion of  intercellular  spaces  filled  with  an  intercellular  fluid. 
The  heart  is  formed  from  two  symmetrical  vessels  in  the 
alimentary  canal  in  the  head  which  represent  the  primitive 
aortae.  These  coalesce  in  the  median  line,  forming  a  tube. 
From  this  tube  the  heart  is  developed  by  the  formation  of 
an  S-like  curve,  whereby  the  tube  is  divided  into  an  auricle, 
ventricle,  and  truncus  arteriosus.  By  a  partition  appearing 
in  the  tube,  the  right  and  left  heart  are  formed.  From  the 
heart  there  spring  originally  two  aortic  arches  which  give 
off  the  omphalo-mesenteric  arteries.  The  branches  of  these 
arteries    pass    through   the   germinal    disk   to   the   sinus    ter- 


PHYSIOLOGY  OF   THE  EMBRYO  3l7 

minalis,  while  veins  proceed  from  the  sinus  to  the  heart. 
The  system  of  vessels  thus  formed  is  called  the  vascular 
area.  Shortly  after  the  heart  is  formed  it  begins  to  beat 
rhythmically,  thereby  setting  in  circulation  the  fluid  formed 
in  the  vascular  system.  It  is  worthy  of  note  that  the  cardiac 
muscle  contracts  rhythmically  at  a  time  when  it  contains  no 
ganglionic  cells. 

By  means  of  the  vitelline  circulation  the  embryo  is  sup- 
plied with  nourishment  which  has  been  taken  up  by  the 
blood  from  the  yolk-sac. 

The  red  blood  corpuscles  originate  from  the  so-called 
blood  islands,  i.e.  groups  of  cells  in  the  cords  from  which 
the  blood  vessels  are  developed.  The  cells  of  the  blood 
islands  form  blood  pigment,  separate,  and  then  appear  as 
nucleated  blood  corpuscles  suspended  in  the  fluid. 

(2)  Placental  circulation. — From  the  abdominal  aorta 
formed  by  the  union  of  the  primitive  aortic  arches  proceed 
the  two  umbilical  arteries  through  the  umbilical  cord  (the 
wall  of  the  allantois)  to  the  place  where  the  allantois  joins 
the  chorion  and  where  the  placenta  originates.  Here  the 
arteries  split  up  into  capillaries.  From  these  capillaries 
the  blood  is  collected  by  the  umbilical  vein,  which  passes 
through  the  umbilical  cord  to  the  navel;  thence,  as  the 
ductus  venosus  Arantii,  under  the  liver  to  the  inferior  vena 
cava. 

At  this  time  the  right  and  the  left  heart  are  not  yet  com- 
pletely separated.  In  the  septum  between  the  auricles  exists 
an  aperture,  the  valvula  Enstachii.  The  pulmonary  arteries 
and  the  aorta  are  still  united  by  one  of  the  primitive  aortic 
arches,*  the  so-called  ductus  Botalli.  Part  of  the  blood  from 
the  right  auricle  passes,  therefore,  through  the  valvula  Eus- 
tachii  directly  into  the  left  auricle  and  thence  into  the  left 
ventricle   and   aorta,  while  part  of  it  passes   from   the   right 

*  Corresponding  to  the  five  pairs  of  gill-arches,  five  pairs  of  aortic  arches  are 
formed  which  undergo  the  following  changes  :  The  first  two  pairs  disappear;  the 
third  pair  forms  the  external  carotids ;  the  fourth  arch  on  the  left  side  forms  the 
aorta,  on  the  right  side,  the  right  subclavian;  the  fifth  on  the  left  side,  the  ductus 
Botalli  and  the  left  pulmonary  artery  ;  on  the  right  side  the  right  pulmonary- 
artery. 


318  HUMAN  PHYSIOLOGY 

auricle  into  the  right  ventricle  and  pulmonary  artery  and 
thence  directly  through  the  ductus  Botalli  into  the  aorta. 
Only  a  small  part  of  the  blood  pases  through  the  lungs  of 
the  embryo.  This  peculiar  arrangement  of  the  blood  vessels 
becomes  clear  when  we  recollect  that  the  exchange  of  gases 
in  the  embryo  does  not  take  place  in  the  lungs  and  that 
consequently  only  so  much  blood  needs  to  flow  through  the 
lungs  as  is  sufficient  to  provide  for  their  nourishment  and 
growth.  After  birth,  when  pulmonary  respiration  begins, 
the  division  between  the  auricles  of  the  heart  is  completed 
and  the  ductus  Botalli  is  obliterated. 

The  placenta  is  a  very  vascular  structure,  composed  of 
two  united  parts,  one  part  the  maternal,  the  other  the  fcetal, 
portion.  The  vascular  villi  of  the  fcetal  portion  extend  into 
spacious  blood  cavities  formed  by  the  dilated  capillaries  of 
the  maternal  portion.  This  great  abundance  of  vessels  in 
the  placenta,  part  of  which  belong  to  the  fetus  and  part  to 
the  mother,  makes  a  rapid  exchange  of  gases  between  the 
maternal  and  the  fcetal  blood  possible. 

The  formation  of  red  blood  corpuscles  during  the  placental 
circulation  takes  place  chiefly  in  the  liver  and  spleen  of  the 
embryo. 

During  the  middle  of  pregnane}-  the  cardiac  sounds  of  the 
embryo  can  be  heard  at  different  parts  of  the  uterus  accord- 
ing to  the  position  of  the  embryo.  The  double  sound  is 
often  accompanied  by  noises  caused  by  the  circulation  of 
blood  in  the  umbilical  cord.  The  rate  of  the  cardiac  sounds. 
of  the  embryo  is  120-160  in  a  minute.  It  is  increased  by 
movements  of  the  embryo. 

{l>)  Respiration. — In  regard  to  the  respiration  of  the  em- 
bryo, two  periods  con  be  distinguished.  During  the  first 
period  corresponding  to  the  vitelline  circulation  the  supply- 
ing of  oxygen  and  removal  of  carbon  dioxide  is  not  brought 
about  by  any  special  organs.  Real  respiration  begins  with 
placental  circulation.  The  taking  up  of  oxygen  and  giving 
off  of  carbon  dioxide  does  not  take  place  in  the  lungs  but  in 
the  placenta.      The  oxygen  is  supplied  by  the  arterial  blood 


PHYSIOLOGY   OF    THE   EMBRYO  319 

of  the  mother,  and  the  carbon  dioxide  of  the  embryo  is  taken 
up  by  it. 

Metabolism  and  the  corresponding  need  of  oxygen  in  the 
embryo  is  small.  The  exchange  of  gases  in  the  placenta  is 
sufficient  to  maintain  the  embryo  in  apncea.  But  this  con- 
dition ceases  immediately  when,  by  compression  of  the 
umbilical  cord  or  by  premature  rupture  of  the  placenta,  the 
normal  exchange  of  gases  in  the  blood  of  the  embryo  is. 
stopped.  The  blood  of  the  embryo  then  lacks  oxygen, 
while  the  carbon  dioxide  accumulates  by  which  the  respira- 
tory centre  is  stimulated  and  premature  respiratory  move- 
ments are  made. 

The  lungs  of  the  embryo  are  developed  from  two  divertic- 
uli  of  the  ventral  Avail  of  the  esophagus  and  contain  no  air 
(atelectatic);  the  alveoli  are  formed,  but  are  collapsed,  i.e. 
filled  by  cuboidal  epithelial  cells.  Xo  negative  pressure- 
exists  in  the  pleural  cavity.  When  by  the  first  inspira- 
tory movement  after  birth  air  is  forced  in,  the  epithelial  cells 
of  the  alveoli  are  flattened,  the  alveoli  contain  air,  and,  after 
some  time,  negative  pressure  is  developed  in  the  pleural 
cavity.  As  to  the  origin  of  this  negative  pressure  authors  do 
not  agree. 

(c)  Nutrition  of  the  embryo. — All  the  nourishment  which 
the  embryo  needs  for  its  metabolism  and  growth  is  derived 
from  the  mother  organism.  In  regard  to  nutrition  we  can 
distinguish  two  periods,  one  of  which  corresponds  to  the 
vitelline  circulation,  the  other  to  placental  circulation. 
During  the  first  period  the  embryo  is  supplied  with  food  by 
the  blood  of  the  yolk-sac.  The  food  transudes  from  the 
vessels  of  the  mucous  membrane  of  the  uterus  through  the 
mucosa  and  egg  membranes  to  the  yolk-sac.  During  the 
placental  circulation,  however,  the  embryo  takes  its  food 
from  the  blood  of  the  mother  present  in  the  placenta.  The 
food  transudes  from  the  maternal  vessels  of  the  placenta  into 
the  foetal  placental  vessels.  As  the  yolk-sac  is  of  no  further 
importance  after  the  completion  of  the  placental  circulation, 
it   gradually  diminishes  in    size  and   finally  dwindles    away 


S2o  HUMAN  PHYSIOLOGY 

almost    entirely,    what    is    left    being    called    the    umbilical 
vesicle. 

{d  )  Secretions  of  the  embryo. 

i.  Meconium. — Meconium  is  a  dark  brownish-green  mass 
having  the  consistency  of  pitch.  It  is  found  in  the  intestine 
of  the  embryo,  from  which  it  is  discharged  soon  after  birth. 
It  contains  20-28^  solids,  which  include  mucin,  bile  acids, 
bile  pigments  bilirubin  and  biliverdin,  but  no  hydrobili- 
rubin),  cholesterin,  fats,  soaps.  Substances  in  the  faeces  of 
the  adult  which  indicate  intestinal  putrefaction  are  lacking 
in  meconium.  Meconium  may  be  regarded  as  a  solidified 
secretion  of  the  glands  of  the  intestines,  and  its  composition 
indicates  that  the  liver  is  the  chief  seat  of  its  formation. 

The  liver  is  formed  early  by  diverticuli  of  the  intestinal 
wall  in  the  form  of  the  primitive  liver  ducts,  which,  by 
branching,  form  the  smaller  bile  passages.  The  liver  secre- 
tions take  place  as  earl}-  as  the  third  month. 

2.  Formation  of  amniotic  fiuid. —  The  amniotic  fluid  is 
found  in  the  amniotic  cavity  and  surrounds  the  embryo.  It 
has  a  weak  alkaline  reaction  ;  its  specific  gravity  varies  con- 
siderably, I.002— 1.028.  It  contains  some  proteids,  salts, 
urea,  allantoin,  and  kreatinin.  The  amniotic  fluid  is  formed 
not  only  by  the  embryo,  but  also  by  the  mother  organism. 
That  part  of  this  fluid  is  derived  from  the  mother  organism 
is  proved  by  tlie  fact  that  sodium  sulphindigotate  injected 
into  the  mother  organism  is  found  in  the  amniotic  fluid,  but 
not  in  the  embryo.  Still  the  amniotic  fluid  is  partly  an 
excretion  product  of  the  embryo,  the  urine  of  the  embryo 
being  discharged  into  the  amniotic  cavity. 

In  the  development  of  the  urinary  organs,  the  pro- 
nephros, or  Wolffian  bodies,  are  first  formed.  These  arc 
glandular  organs  lying  on  either  side  of  the  vertebral  column. 
They  are  composed  of  coiled  uriniferous  tubules  which 
earn',  at  their  closed  end.  a  glomerulus  and  at  the  other 
end,  open  into  a  common  duct,  the  Wolffian  duct.  This 
duct  opens  into  the  cloaca,  whose  anterior  end  forms  the 
urethra  by  the   formation   of    the    perineum.      Later  on   the 


PHYSIOLOGY   OF   THE   EMBRYO  321 

permanent  kidneys  are  formed  by  the  diverticuli  of  the 
posterior  end  of  the  Wolffian  duct.  These  diverticuli  branch 
and  the  branches  become  the  uriniferous  tubules  of  the  kid- 
neys ;  at  their  closed  ends  a  glomerulus  forms.  In  the 
female  the  Wolffian  duct  is  obliterated,  while  in  the  male  it 
forms  the  vas  deferens. 

3.  The  sebaceous  secretion  begins  in  the  fifth  month. 
The  substance  thus  secreted  forms  a  fatty  layer  upon  the 
skin  and  is  called  the  vernix  caseosa. 

The  removal  of  metabolic  waste  products  from  the  embryo 
is  accomplished  not  only  by  the  glands  (liver  and  kidneys), 
but  also  by  the  exchange  of  gases  between  the  foetal  and 
the  maternal  blood  in  the  placenta. 

(/)  Metabolism. — The  metabolism  of  the  embryo  is  small; 
little  heat  needs  to  be  produced,  for  the  loss  of  heat  is  ex- 
ceedingly small.  The  muscular  movements  which  could 
increase  metabolism  are  very  limited.  Hence  the  food  sup- 
plied to  the  embryo  is  chiefly  used  for  its  growth. 

3.     THE    TRANSFORMATION    AND    SETTING    FREE    OF 
ENERGY   IN   THE    EMBRYO 

(a)  Muscular  movements. — The  first  appearance  of  the 
skeletal  muscle  is  during  the  second  month  of  pregnane)*. 

Muscular  movements,  excepting  the  beat  of  the  heart, 
begin  at  the  fifth  or  sixth  month.  They  consist  of  jerky 
movements  of  the  limbs  against  the  walls  of  the  uterus. 
The  movements  of  the  foetus  appear  to  be  reflex  movements  ; 
they  are  increased  when  the  foetus  is  pushed  by  pressing  upon 
the  abdominal  walls  of  the  mother.  At  the  close  of  preg- 
nancy, weak  rhythmic  respiratory  movements  are  sometimes 
made,  also  movements  of  sucking  and  deglutition  ;  swallowed 
amniotic  fluid  may  be  found  in  the  embryo. 

(b)  The  development  of  the  functions  of  the  nervous 
system. — The  researches  concerning  the  medullation  of  the 
nerves  furnish  the  basis  for  judging  the  development  of  these 
functions.      The    nerve    fibres    at    first   have    no    medullary 


322  HUMAN  PHYSIOLOGY 

sheath,  but  acquire  this  structure  later  on,  and  nerve  fibres 
of  different  functions  acquire  it  at  different  periods.  The 
development  of  the  medullar}'  sheath  can  be  readily  investi- 
gated, for  the  medullated  nerve  fibres  are  white,  while  the 
fibres  not  containing  this  sheath  appear  gray.  It  may  be 
assumed  that  the  function  of  the  nerve  fibre  is  only  com- 
pletely present  when  the  nerve  sheath  has  been  formed. 

In  the  spinal  cord  the  medullar)'  sheaths  of  the  anterior 
and  posterior  roots  are  first  formed,  i.e.  the  tracts  serving 
for  reflex  actions.  After  this,  the  sheaths  of  the  antero- 
eround,  the  lateral  "'round  bundle,  and  of  Burdach's  column, 
i.e.  bundles  which  contain  fibres  chiefly  for  the  indirect 
reflex  tracts.  Then  the  sheaths  of  the  long  sensory  tracts 
leading  to  the  brain  are  formed,  and  finally  the  sheath  of  the 
long  motor  tracts  leading  from  the  brain.  From  the  succes- 
sive developments  of  the  medullar}'  sheaths  it  is  evident 
that,  in  the  spinal  cord,  the  simpler  reflexes  appear  first;  next 
the  more  complicated  and  radiated  ;  and  finally  the  paths 
for  the  stimuli  causing  sensations  and  voluntary  movements. 

In  the  corona  radiata,  the  centripetal  fibres  for  the  sensory 
areas  of  the  cerebral  cortex  are  developed  before  the  corre- 
sponding centrifugal  fibres;  hence  the  conditions  for  the 
formation  of  sensations  are  perfected  before  those  for  the 
formation  of  voluntary  movements.  Some  of  the  fibres  for 
the  sensory  areas  develop  after  birth  (see  page  329). 

In  the  medulla  oblongata,  however,  there  appear  at  an 
early  date  groups  of  cells  whose  axis-cylinder  processes 
course  down  the  anterior  and  lateral  columns  of  the  cord 
(hence  centrifugal  fibres) ;  these  fibres  are  already  medul- 
lated when  the  sensor)'  roots  of  the  medulla  have  no  medul- 
lary sheaths.  These  cells  and  fibres  are,  therefore,  well 
developed  and  function  at  the  time  when  the  posterior  roots 
still  appear  embryonic.  This  indicates  that  the  action  of 
centres  is  automatic  and  not  reflex.  The  sensory  nerves, 
when  fully  developed,  stimulate  and  eventually  regulate  the 
centres  which,  prior  to  this,  were  already  active.  It  must 
be    remembered    that   the    medulla    contains    the    important 


PHYSIOLOGY   OF   THE  EMBRYO  323 

nerve  centres  which  maintain  the  vegetative  functions  of  the 
body. 

Little  need  to  be  said  concerning  the  physiological  devel- 
opment of  the  sense  organs.  The  only  sensations  which 
can  come  into  account  in  the  fcetal  life  are  the  tactile,  pain, 
and,  perhaps,  some  organ  sensations.  These  evidently  call 
forth  the  movements  of  the  foetus. 

4.    DIFFERENTIATION    OF    SEXES 

The  reproductive  organs  are  developed  as  follows:  On 
the  ventral  side  of  the  pronephros,  the  genital  ridge  and  a 
special  duct,  Midler's  duct,  running  parallel  with  the 
Wolffian  duct  and  also  opening  into  the  cloaca,  are  formed. 
In  the  male  the  genital  ridge  forms  the  testis,  the  pronephros 
forms  the  hydatid  of  the  epididymus,  the  Wolffian  ducts  the 
vas  deferens  ;  the  duct  of  Muller  is  obliterated  except  a  small 
rudiment,  called  the  uterus  masculinus.  In  the  female  the 
genital  ridge  becomes  the  ovary,  Midler's  duct  the  oviduct; 
and  the  mouth  of  the  Mailer's  duct  at  the  cloaca  dilates  and 
forms  the  uterus.  The  Wolffian  duct  disappears.  Nothing 
is  known  concerning:  the  causes  of  sexual  differentiation. 


CHAPTER    XXIX 
PREGNANCY.     PARTURITION.     CHILDBED 

DURING  the  development  of  the  foetus  in  the  uterus,  the 
following  changes  occur  in  the  maternal  organism :  The 
muscle  fibres  of  the  uterus  increase  in  size  and  number  and 
the  whole  uterus  increases  enormously.  In  the  virgin  state 
the  uterus  is  7  cm  long,  3.2  cm  broad,  and  weighs  30  g;  at 
the  end  of  pregnancy  it  is  37  cm  long,  26  cm  wide,  and 
weighs  about  1  kg.  The  intramuscular  connective  tissue 
loosens  and  increases  and  the  blood  vessels,  nerves,  and 
lymph  vessels  also  increase.  The  mucous  membrane  of  the 
uterus  thickens  and  grows  over  and  covers  the  egg,  forming 
the  decidua.  That  part  of  the  wall  of  the  uterus  which 
grows  over  the  egg  is  called  the  decidua  reflexa,  while  the 
part  bordering  upon  this  is  called  the  decidua  vera.  The 
placental  part  of  the  decidua  vera  is  called  the  decidua  sero- 
tina.  As  the  uterus  increases  it  fills  the  pelvic  cavity  and 
forces  the  intestines  aside  and  the  diaphragm  upward. 
During  pregnane}-  ovulation  and  menstruation  cease. 

The  breasts  begin  to  increase  in  size  during  the  first 
months  of  gestation,  the  nipple  and  the  areola  assume  a  dark 
color,  the  milk  glands  yield  spontaneously  or  upon  pressing 
a  light-colored  water)'  fluid. 

Metabolism  is  increased  during  pregnancy. 

The  period  of  gestation  reckoned  from  the  day  of  the  last 
menstruation  is  about  270-280  days. 

Parturition  is  effected  by  the  contraction  of  the  muscles 
of  the  uterus  by  which  pressure  is  exerted  upon  the  contents 
of  the  uterus.      The  pressure  thus  produced  may  be  as  much 

32+ 


PREGNANCY.     PARTURITION.     CHILDBED.  325 

as  100  mm  Hg.  By  these  contractions  the  foetus  is  pressed 
against  the  cervical  canal,  which  dilates  and  stretches  so  that 
the  uterus  and  the  vagina  form  a  common  tube.  The  mem- 
brane of  the  egg  (the  decidua  reflexa  of  the  utrinal  mucous 
membrane,  the  chorion  and  the  amnion)  are  ruptured  so 
that  the  amniotic  fluid  is  discharged.  By  further  contraction 
of  the  uterus  the  child  is  forced  through  the  vagina  and 
pelvis,  generally  head-foremost.  Parturition  is  aided  by 
compression  of  the  abdomen.  Soon  after  the  birth  of  the 
child  the  placenta  is  loosened  by  the  further  contraction  of 
the  walls  of  the  uterus  and,  under  loss  of  some  blood,  is 
discharged  with  the  egg  membranes  (after  birth;. 

The  innervation  of  the  uterus  takes  place  by  means  of  the 
nerves  from  the  lowest  thoracic  and  from  the  lumbar  cord. 
A  part  of  the  fibres  pass  through  the  sympathetic,  while 
another  part  pass  directly  with  the  sacral  nerves  to  the 
uterus.  The  centre  for  the  contraction  of  the  uterus  lies  in 
the  lumbar  cord.  This  centre  can  be  stimulated  reflexly  by 
stimulations  from  the  centripetal  nerves  of  the  uterus.  These 
centripetal  nerves  are  stimulated  by  the  tension  in  the  walls 
of  the  uterus  caused  by  the  growing  foetus.  In  dogs  in 
which  the  lumbar  cord  is  separated  from  the  rest  of  the 
nervous  system,  normal  parturition  can  still  take  place. 

The  duration  of  parturition  varies.  In  case  of  the  first- 
born it  may  last  20  hours,  but  in  subsequent  cases  it  is 
shorter.  During  parturition  the  contractions  of  the  uterus 
gradually  become  more  intense,  frequent,  and  longer  until 
the  child  is  expelled.  These  contractions  are  accompanied 
by  pain.  During  each  "pain"  the  temperature,  rate  of 
pulse,  and  perspiration  are  increased. 

After  parturition  the  uterus  assumes  its  normal  form, 
many  of  the  muscle  cells  undergoing  fatty  degeneration. 
The  inner  surface  of  the  uterus  acquires  a  new  epithelial 
lining,  and  after  about  four  weeks  the  regeneration  of  the 
mucous  membrane  is  complete.  As  long  as  a  mucous  mem- 
brane is  not  regenerated,  it  behaves  like  a  wound  and 
secretes  a  corresponding  wound  secretion.      This  secretion 


326  HUMAN  PHYSIOLOGY 

which  is  cast  out  is  called  lochia.  The  lochia  is  bloody 
during  the  first  days,  during  the  fifth  day  it  is  serous,  later 
on  it  becomes  grayish. 

The  breasts  swell  much  during  the  second  and  third  days 
after  parturition.  The  first  secretion — colostrum — is  a  thick, 
yellowish  fluid,  containing  colostrum  corpuscles  (see  page 
112);  at  the  third  day  real  milk  is  secreted.  The  period  of 
lactation  lasts  about  ten  months,  and  during  this  time 
menstruation  does  not  take  place. 


CHAPTER    XXX 
DEVELOPMENT    OF   THE   BODY    AFTER    BIRTH 

1.    INFANCY 

DURING  infancy  the  body  is  nourished  by  fluids  only, 
chiefly  by  milk.  As  the  formation  of  the  first  teeth  is  con- 
nected with  the  ability  to  take  up  solid  food,  the  period  of 
infancy  extends  from  birth  till  the  first  dentition. 

(a)  Circulation  and  respiration  of  the  infant. — Imme- 
diately after  birth  the  circulation  in  the  umbilical  vessels 
ceases,  and  the  umbilical  cord  constricts.  If  it  is  then  cut, 
no  bleeding,  as  a  rule,  results,  yet  to  prevent  possible  bleed- 
ing it  is  ligatured  and  cut.  Animals  cut  the  umbilical  cord 
with  their  teeth.  The  part  of  the  umbilical  cord  left  attached 
to  the  child  dries  up  and  falls  off  after  a  few  days.  The 
navel  discharges  matter  for  some  time  and  heals  after  12—14 
days. 

Immediately  after  birth  the  first  inspiration  is  made.  The 
alveoli  of  the  lungs  fill  with  air  and  their  epithelial  cells 
become  flattened.  Simultaneously  the  blood  streams  more 
abundantly  through  the  vessels  of  the  lungs.  Gradually  the 
ductus  arteriosus  Botalli  is  obliterated  and  the  septum 
between  the  auricles  is  completed.  The  remains  of  the 
umbilical  arteries  and  veins  degenerate  to  connective  tissue. 

The  rate  of  the  pulse  during  the  first  week  is  120—140  per 
minute;  during  the  second  year  110.  The  number  of  res- 
pirations in  the  new-born  is  44  per  minute ;  during  the  third 
year  35-40. 

{b)  Nutrition  and  growth  of  the  infant.  -The  normal 
nourishment  for  the  infant  is  the  milk  of  the  mother.  The 
replacement  of  this  by  other  food  (e.g.  cow-milk  or  artificial 

327 


3 2k  HUMAN  PHYSIOLOGY 

preparation)  must  be  regarded  as  makeshifts  and  are  often 
not  suited  for  the  child.  The  average  amount  of  milk  which 
the  infant  takes  is  as  follows:  During  first  da}-  30  grams, 
second  day  150,  third  day  400,  fourth  da)-  550  grams;  after 
one  month  650,  three  months  750,  four  months  850,  six  to 
nine  months  950  grams. 

The  length  of  the  body  of  the  child  at  birth  is  about 
50  cm. 

The  infant  grows  during  the  first  month  4  cm,  during  the 
second  month  3  cm,  during  the  third  month  2  cm,  and 
during  the  following  months  1-1.5  cm.  The  total  increase 
in  length  during  the  first  year  is  about  20  cm,  during  the 
second  year  9  cm,  and  during  the  third  year  7  cm.  The 
weight  after  birth  is  3  kg.  Immediately  after  birth  the  infant 
loses  from  100-300  grams  of  its  body  weight.  After  this  its 
weight  increases  and  after  the  tenth  da}'  it  has  regained  its 
previous  weight.  During  the  first  five  months  the  weight 
of  the  normally  nourished  child  increases  on  the  average  20 
to  30  grams  daily;  during  the  next  seven  months  10-15 
grams  daily.      After  one  year  the  child  weighs  about  9  kg. 

During  the  first  days  after  birth  the  child  discharges  the 
meconium  through  the  anus.  Later  on  the  stools  of  the 
normally  fed  child  are  yellowish  and  of  medium  consistency. 

(V)  The  nervous  system  and  the  senses  of  the  infant. — 
Concerning  the  physiological  development  of  the  central 
nervous  system  during  infancy  the  following  maybe  said: 
At  birth  certain  reflex  and  coordinated  movements,  those 
necessary  for  the  maintenance  of  life  (respiration  movements, 
sucking,  deglutition)  are  present.  Sucking  takes  place 
reflexly  when  a  foreign  body  touches  the  lips.  The  coordi 
nated  movements  which  play  a  part  in  standing  and  walking 
are  not  present  in  the  human  infant  immediately  after  birth, 
but  are  learned  during  the  first  or  second  year.  This  is  also 
true  for  the  coordinated  movements  for  speech.  The  reflex 
irritability  is  greater  in  the  infant  than  in  the  adult.  Reflex 
cramps  can  be  produced  by  relatively  feeble  stimulation  of 
sensor}-  nerves  (e.g.  convulsions  during  dentition,  tetanus). 


DEVELOPMENT   OF    THE  BODY  AFTER  BIRTH  329 

At  birth  the  conducting  fibres  for  the  sensory  areas  of  the 
cerebral  cortex  are  not  all  medullated.  The  tracts  for  the 
visual  centre  develop  their  sheaths  at  the  time  of  birth,  while 
those  of  the  auditory  area  are  developed  after  birth.  The 
fibres  of  association  develop  about  three  months  after  birth. 

As  to  the  development  of  the  senses  the  following  facts 
may  be  stated  in  regard  to  sight.  During  the  fifth  week, 
fixation,  associated  movements  of  the  eyes,  closure  of  the 
eyelids  when  the  macula  lutea  is  illuminated,  and  accommo- 
dation take  place.  Only  during  the  fifth  month  is  there  a 
development  of  orientation  of  the  visual  field  and  closure  of 
the  eyelids  when  the  periphery  of  the  retina  is  illuminated. 
Until  the  fifth  month  the  eccentric  visual  sensations  are  not 
utilized.  The  child,  therefore,  appears  as  if  it  had  an  ex- 
tremely limited  visual  field.  An  object  upon  which  the  gaze 
is  fastened  is,  during  the  fifth  month,  followed  by  the  eyes, 
but  moving  objects  upon  which  the  gaze  is  not  fixed  do  not 
call  forth,  during  the  first  period,  fixation  of  the  eye.  At 
first  the  infant  does  not  see  the  objects  as  solid  objects  and  it 
lacks  all  judgment  of  size  and  distance.  (The  child  reaches, 
e.g.,  for  the  moon.)  It  is  also  asserted  that  at  birth  the 
sense  of  color  is  absent,  and  that  this  begins  to  develop  during 
the  sixteenth  month  and  is  completely  developed  in  the  fifth 
or  sixth  year.  The  color  sensations  are  first  developed  at 
the  centre  and  later  on  at  the  periphery  of  the  retina. 

The  other  senses  function  immediately  after  birth,  but  it 
is  said  that  the  sense  of  hearing  is  then  incompletely  devel- 
oped ;  this  corresponds  to  the  imperfect  development  of  the 
tracts  of  the  auditory  centre  in  the  new-born. 

The  change  from  infancy  to  childhood  is  marked  by  the 
first  dentition.  The  first  teeth,  the  so-called  milk-teeth, 
develop  in  the  following  order: 

Between  seventh  and  eighth  month  the  lower  central  in- 
cisors. 

Between  eighth  and  tenth  month  the  four  upper  incisors. 

Between  twelfth  and  fourteenth  month  the  four  small 
inner  molars  and  the  two  lower  outer  incisors. 


33°  HUM/IN   PHYSIOLOGY 

Between  eighteenth  and  twentieth  month  the  four 
canines. 

Between  twenty-fourth  and  thirty-fourth  month  the  four 
smaller  outer  molars. 

Between  the  age  of  4.5-  and  5  years,  the  first  four  large 
permanent  molars  appear. 

2.    CHILDHOOD 

Childhood  extends  from  the  first  dentition  to  puberty. 
During  this  period  the  physiological  functions  are  about  the 
same  as  in  the  adult  human  being,  except  that  metabolism 
is  relatively  greater  than  in  the  adult,  as  already  explained 
see  page  I  18),  and  that  the  sexual  functions  are  not  present. 
The  second  dentition  takes  place  during  childhood.  It 
begins  during  the  seventh  year  and  extends  to  the  fifteenth 
year.  The  temporary  teeth  are  replaced  by  the  permanent 
set  and  four  new  large  molars  are  added.  Between  the 
ages  of  eighteen  and  twenty-five,  and  sometimes  still  later, 
the  last  molars,  the  wisdom  teeth,  are  finally  developed. 

The  following  table  shows  the  changes  in  the  length  and 
weight  of  the  body  at  different  ages : 


Birth.  . 

5  year 
10     '• 
15      •• 
20     " 
30     " 

4"  " 
60  " 
80     " 


Length. 


°-5 
1 .0 

i-3 

1.6 

i-7 

i-7 

i-7 

1.65 

1.6 


Weight, 
kg. 


lS 

2  5 
44 
60 

65 
^5 
62 

58 


Woman. 


Length 


°-5 

0.95 

1 .2 

i-5 

1.6 

1.6 
1.6 
1.52 
i-5 


Weight, 
kg. 


14 
24 
40 

52 

55 
55 
54 
49 


3.    PUBERTY 


Puberty  is  the  period  of  sexual  maturity,  which  begins  at 
the  age  between  fourteen  and  seventeen.     It  is  characterized 


DEVELOPMENT   OF   THE  BODY  AFTER   BIRTH  331 

by  many  changes  in  the  body.  In  the  male  the  formation 
of  spermatozoa  and  beard  take  place,  the  larynx  develops 
more  powerfully,  and  the  voice  changes.  Sexual  desires 
awaken.  The  manly  character  appears.  In  castrated 
children  these  phenomena  are  not  observed.  Female 
puberty,  which  occurs  a  little  earlier  than  in  the  male,  is 
accompanied  by  ovulation  and  menstruation,  and  the  external 
sexual  organs  are  covered  with  hair  and  the  mammary 
glands  develop. 

4.   OLD    AGE,    DEGENERATION,    AND    PHYSIOLOGICAL 

DEATH 

The  prime  of  life  in  man  extends  from  the  twenty-fifth  to 
the  forty-fifth  year.  After  this  degeneration  sets  in,  the 
body  weight  and  length  decrease.  Metabolism  and  the 
functions  of  the  organs  are  reduced.  In  high  old  age  a  great 
debility  of  the  organs,  especially  of  the  brain  and  heart,  sets 
in,  which  finally  results  in  physiological  death  or  death  by 
senile  decay.  In  the  female  this  degeneration  begins  with 
the  climacteric,  the  cessation  of  ovulation  and  menstruation. 
The  greatest  old  age  in  man  may  be  over  one  hundred 
years.  According  to  the  mortuary  statistics,  the  average 
length  of  human  life  in  civilized  countries  is  thirty  years. 


INDEX 


Absorption,  140 
Accommodation,  262 

centre  of,  242 
Acetone,  42,  105 
Action-currents,  194,  217 
Adamkiewicz'  test,  30 
Adaptation,  8 
Adenin,  48 
Adipose  tissue,  14 
After-images,  272.  273,  276 
Albuminoids,  38 
Albumins,  31 
Albumoses,  36,  37,  129 
Alcohol,  118,  122 
Alexines,  57 

Alimentary  principles,  114 
Alkali  albumin,  31 
Allantois,  315 

Alternation  of  generation,  7 
Amido  acids,  27,  136 
Ammonia,  43,  104,  196,  219 
Amnion,  315 
Amniotic  fluid,  320 
Amylopsin,  133 
Anelectrotonus,  220 
Animal  heat,  174 

Anterior  ground  bundle,  226-229,  237 
Antipeptones,  38 
Antitoxins.  57 
Apex  beat,  68 
Apncea,  84 

Aqueous  humor,  260,  284 
Arginine,  27 

Aromatic  compounds,  51,  136 
Articulations  of  bones,  201 
Arytenoid  cartilage,  209 
Ash  in  tissues,  15 
Aspartic  acid,  27 
Asphyxia,  85,  240 
Assimilation,  2,  6,  140 
Association  centres,  247 

fibres,  237 
Astigmatism,  266 
Atropin,  75.  107,  no 


Auditory  centre,  246 

nerve,  252,  292,  295 

ossicles.  286 

sensation,  292 
Auricles  of  heart,  67 
Auto-digestion  of  stomach,  131 
Automaticity,  224 
Axis-cylinder,  215 

Bacteria,  metabolism  of,  2 
Balance  of  nutrition,  155,  161 
Ball-and-socket  joint,  202 
Basal  ganglia.  240 
Bell's  law.  250 
Bile,  99.  101,  135.  145 
acids,  49,  too 
pigments.  50,  100 
Bilirubin,  50,  100 
Biliverdin,  50.  100 
Binocular  vision.  281 
Biostition,  4 
Biuret  reaction.  30.  38 
Blind  spot.  271 
Blood,  14,  16.  52 

color  of.  59 

corpuscles,  52,  53 

flow,  71,  73 

gases,  58 

loss  of,  78 

platelets.  55 

pressure,  73,  78,  152 

and  respiration,  71 
"        in  heart,  67 
"        in  vessels,  69 

reaction  of,    52,  59 
Body  temperature,  180,  242 
Bone  marrow.  54 
Bones  14,  16,  201 
Border  cells.  93 
Bottger's  test,  19 
Brain,   14,  16,  235 
Burdach's  column,  226,  237 


Calcium  13,  17,  115 


333 


334 


INDEX 


Calorie.  178 

Canalis  cochleae,  289.  290 

Cane-sugar,  21.  131,  146 

Carbohydrates.  136,  159,  186 

absorption  of,  145 
classification  of,  18 
composition  of,  18 
digestion  of,  124,  133, 

functions  of,  116,  169 
in  blood,  57 

Carl),  in,   12 

dioxide,  42.  58.  85,  159,  187 

equilibrium,   158 
Cardiac  accelerating  centre,  238 
nerve,  75 

cycle.  65 

impulse,  68 

inhibitory  centre,  238 
nerve.   74 

muscle,  04.  66.  191 

sounds.  68.  318 
Cardinal  points,  262 
Cardiogram,  68 
Carnic  acid.  186.  187 
Camin.  40 

Caseinogen,  36,  131.   143 
Cells,  5^6 

division  of.  7 
Cellulose,  22,   120,   136 
Cerebellar  tracts,  226-229.  23^ 
Cerebellum.  240 
Cerebro-spinal  fluid,  14,  249 
Cerebrum,  243 
Cheese,   120 
Chematropism.  200 
Chief  points,  261 
Chlorine,  13 
Chlorophyll.  2,  3 
Cholesterin.  25 
Chondrin,  40 
Chorion,  315 

Chromatic  aberration,  266 
Chyle,  87 
Ciliary  movements,  200 

muscles,  264 
Circles  of  diffusion.  262 
Circulating  proteids,  32 
Circulation  oi  Mood,  63,  316 

time.   74 
Coagulation  of  blood,  52.  57 

proteids  of,  2S 
Cochlea,  288 
Cochlear  nerve,  292 
CO-haemoglobin,  33 
Cold,  sensation  of.  302 
Collagen,  40 
Color  blindness,  275 


( !olor  sensations,  274 
Colostrum,  112,  326 
Combined  proteids,  32,  130 
Combustion,  physiological,  61,  172 
Commissural  fibres,  237 
Compensatory  movements,  240 

pause,  05 
Complemental  air,  82 
Complementary  colors,  275 
Conductivity  of  nerves,  216-221 
Conjugated  points.  258 
Consensual  pupil  reflex,  268 
( lonsonance,  293 
Consonants,  214 
Contraction  of  muscles.   18S-I99 
Convulsion  centre.  240 
Corona  radiata,  235-237,  245-247- 
Corpora  quadrigemina,  236.  241 
Corpus  callosum,  237 
Corti,  organs  of.  290 
Cranial  nerves.  236.  250 
Cricoid  cartilage,  209 
Crypts  of  Lieberkiihn,  103 
Curare.  75.   147.  196 
Cystin.  49 

I  > arwinian  theory,  8 

Death,  6 

Defecation,  138,  234 

I  teglutition,  125.  239 

Dendrites,  215 

Dentition.  329 

Depressor  nerve,  77 

Deuteroalbumose,  129 

Development,  6-9,  313 

Dextrin,  22 

Dextrose  (see  Crape  Sugar). 

Diabetes,  42,   105,   147,   153.  240 

Diapedesis,  200 

Diaphragm,  79 

I  (iastole,  63,  65 

Dicrotic  wave,  71 

Diet,  117,  121.  171 

Difference-threshold.  256 

Differentiation  of  cells,  6 

Digestion.  123.  138 

effect  011  metabolism,   174 
Digital!'-.   75 
Diopter-.  265 
Dioptric  mechanism,  257 
Diplopia,  281 
1  ^saccharides,  21 

Dissimilation,  2,  6  (see  Metabolism). 
Diuretics,  107 
Ductus  Botalli,  317 
Dyspnoea,  42,  85 

Ear,  285 
Ectoderm,  313 


INDEX 


335 


Elastin,  4° 

Electrotonus,  219,  220 
Elements  found  in  body,  12 

Embryo,  313  .  <- 

circulation  in,  310 

development  of,  315 

metabolism  of,  319 

respiration  of,  84,  31b 
Emmetropia,  266 
Endoderm,  313 
Energy,  2,  3-  H4  F77 
Entoptical  vision,  267 
Eupncea,  84 
Eustachian  tube,  288 
Extensibility  of  muscle,  180,  192 

Eye,  257  .        „ 

circulation  in,  2&j 

movements  of,  242,  278 

muscles  of.  279 
Eyelids,  242,  283 

Facial  nerve,  251 

Fseces.  137 

Fat  formation.  171 

Fatigue,  4,  19°:  198-222 

Fats,  23,116,  134,  136,  144,  159.  169, 

186 
Fechner's  law.  256 
Fellic  acid.  50 
Fermentation,  20,  22,  41 
Ferments,  40 
Ferratin,  100 
Fertilization,  7,  312 
Fibrin,  56 
Fibrinogen,  56 
Field  of  vision,  278 
Fillet,  236 
Fluorine,  14 
Focal  distance,  259 

points,  259 
Foods,  118,  138 

heat  value  of,  170 
Forced  movements,  241,  295 
Fovea  centralis,  270,  277 

Galvanotropism,  200 
Gastric  digestion,  127 
juice,  95 
secretion,  96 
Gelatin,  40,  116,  I3° 
•Germinal  disk,  313 

Gestation,  324 

Glands,  91 

Globin,  34 

Globulin,  31 

Glossopharyngeal,  252,  295 

Glottis.  210,  2H 
Glycerine,  23 


Glycocholic  acid,  50,  100 

Glycocoll,  27.  50 

Glycogen,  22,  23,  146,  186,  240 

Glycoproteids,  34 

Glucosamin,  21 

Gmelin's  test,  51 

Goitre,  151 

Goll's  column,  226-229,  235 

Graafian  follicles,  310 

Grape-sugar.  20.  105,  146-  186 

Growth,  6 

Guanin,  47 

Hsematoblasts,  54 
Hsematoidin,  34 
Hsematin,  34-  51 
Hsemin,  34 
Haemoglobin,  32,  52. 
Heart,  14,  16,  64 

beat,  65.  66 

work  done  by 
Heat, 


58,  78,  100,  143 


68 


centres  of,  18 1 
loss  of,  180 
production  of,  178,  193 
regulation  of,  181 
value  of  foods,  178 
sensations  of,  301 
Heller's  test,  29 
Helicotrema,  288 
Hemipeptones,  38 
Hepatin,  100 
Heredity,  8 
Hinge-joint,  203 
Hippuric  acid,  48.  108 
Homocentric  rays,  257 
Homoiothermic  animals,  180 
Horopter,  282 
Hunger,  sensation  of,  306 
Hydrochloric  acid.  15,  95>  97,  I2b 
Hydrogen,  12,  178 
Hypermetropia,  266 
Hypoglossals,  253 
Hypoxanthin,  48,  i°4 

Identical  points,  282 

Inanition,  164 

Index  of  refraction,  257 

Indican,  104 

Indol,  51.  104,  I36 

Infancy,  327 

Inhibition,  4 

of  heart,  74 
of  reflexes,  233 

Inosit,  21 
Intelligence,  243 
Internal  secretion.  149 
Intestinal  juice,  102,  135 


260 


336 


INDEX 


Intestinal  digestion,  132 

Intestine,   14.  16 

Inversion  of  sugars,  21,  131 

Iodine.  14.  151 

his.  267 

Iron,  12,  13,  100.  115 

Irradiation,  274 

Irritability,  3 

of  nerves,  216.  218.  222 
of  muscles.  196,  197 

Isometric  contraction.  188 

Isotonic  contraction.  188 

Jaundice.  102,  105 
Jecorin,  26.  249 

joints,  202 

Katelectrotonus,  220 

Keratin,  39 
Kidneys,  14,  16,  105 
Krause,  end-bulbs  of,  300 
Kreatin,  48 
Kreatinin,  48 
Kresol,  104,  136 

Labyrinth,  288.  294 

Lachrymal  secretion  (see  Tears). 

Lactic  acid,  42,  130.  187 

Lactiferous  glands,  112 

Lactose  (see  Milk  Sugar). 

Larynx,  209 

Latent  period,  189 

Lateral  bundles,  226-229 

Law  of  contraction.  221 

Lecithin,  25 

Legumes,  121 

Leucin,  27 

Leucocytes    (see    White    Blood    Cor. 

puscles). 
Light,  wave  lengths  of,  274 
Liminal  intensity,  256,  297 
Liver,   14,   16.  54,  IOO,  146,  152,  240 
Localization  theory,  243 
Lochia,  326 

Locomotion  of  body,  208 
Locomotor  ataxia.  241 
Lungs,  14,  16,  58 
Luxus  consumption,  1G9 
Lymph.  87 

glands.  55,  88 

Macula  lutea.  270 
Magnesium.   13,  18,  1 15 
Maltose,  21,  1 25 
Mastication,  121 
Meconium,  320 
Medulla  oblongata,  237,  322 


Meibomian  glands,  283 

Melamine,  34 

Menstruation,  311 

Mesoderm,  313 

Metabolism,   1.  155,  187,  249,  319 

end  products  of.    42,   186 
Methsemoglobin.  33 
Micturition.   109.  233 
Milk,   in,   120 

sugar,  21.  146 
Millon's  reaction,  30 
Monosaccharides,  19 
Moore's  test,  20 
Motor  areas  of  brain,  247 
Mucin,  34 
Mulder's  test.  19 
Murexide  test,  46 
Muscarin,  75 
Muscle,   14.  16 

activity  of,   187-204 

composition  of,  185,  186 

irritability  of,  1 96 

physical  properties  of,  186 

plasma,  185 

reaction,  187 

serum,  185 

sounds.   IQI 

structure  of.   184 

tonus.  152 
Muscular  activity,    effect    on   metabo- 
lism. 173 
Myogen,  186 
Myohsematin,  186 
Myopia,  265 
Myosin,  185 

Negative  after-image.  273,  276 

variation.   105.  217 
Nerve  impulse,  2 16 

physiology,  215 
Neurites.  215 
Neurons.  215 
Neuroplasm.  215 
Nicotin,  75 
Nitrogen.  12 

in  blood.  59 
Nitrogenous  equilibrium,  158.  168 

metabolism.  187 
Nodal  point,  259,  261 
Nceud  vital.  84 
Nuclein  bases.  47 
Nucleins,  35.  89 
Nucleo-albumins.  35.   1 16 
Nucleus.  5.  6 

d  [composition  of,  35 

of  nerve  cells.  223 
Nutrition.   114 
Nvstignius.  242 


INDEX 


337 


Oculo-motor  nerve,  251.  265 

Old  age,  331 

Olfactory  cell,  296 

centre,  247 
nerve.  250,  296 

Ontogeny,  8 

Ophthalmometer,  261 

Ophthalmoscope,  268 

Optical  axis.  259 

Optic  nerve,  251 

Optics.  257 

Organogenic  elements.  13 

Organ  sensations,  305 

Otoliths.  295 

Oval  joint,  203 

Ovaries,  154,  310 

Ovoid  cells,  96 

Ovum.  310 

Oxalic  acid,  42 

Oxybutyric  acid,  42,  105 

Oxygen.  157,  172 

in  combustion.  2.  187 
in  human  body,  13 
in  blood.  58 
consumed  daily,  61 
in  muscles.  187 

Oxyhemoglobin,  33,  54,  58 

Oxyntic  cells,  96 

Oxyprotosulphonic  acid,  28 

Pain,  sensation  of,  303 
Pancreas,  14,  16,  153 
Pancreatic  digestion,  133 

juice,  98 

secretion,  99 
Paralytic  secretion,  95 
Paranucleins.  35 
Parturition,  324 
Pathetic  nerve,  251 
Pepsin,  95,  128 
Peptones,  36,  37,  129.  133 
Periscopia,  266 
Peristalsis,  121.  126,  132 
Perspiration,  109.  180-183,  239 
Pettenkofer's  test,  49 
Peyer's  patches.  89 
Phenol,  51,  104.  136 
Phenvlhydrazine,  20 
Phloridzin.  147 
Phosphocarnic  acid,  187 
Phosphorus.  13,  43,  147 
Phylogeny.  8 
Pilocarpin.  no 
Pineal  gland.  243 
Placenta,  312,  315.  318 
Placental  circulation,  317 
Plants,  assimilation  in,  2 
Plasma.  52,  55 


Plethysmograph.  72 

Poisons  arrested  by  liver,  153 

Polysaccharides,  22 

Portal  vein.  141 

Positive  after-image.  272 

Potassium.  13.  115 

Presbyopia,  265 

Pressor  nerves,  77 

Pronephros,  320 

Pronucleus,  312 

Protagon,  26.  223.  249 

Protamine.  28 

Proteids.  26.  31.  173 

absorption  of.  142 
decomposition  of,  27.  136 
digestion  of,  128,  133 
functions  of,  30,  116.  167.187 
reaction  of,  28 

Proteoses.  36.  142 

Protoplasm.  5 

Psycho-physical  processes.    231,   237, 
243.  247.  248 

Ptomains,  28 

Ptyalin.  93.  134 

Puberty,  330 

Pulse.  70 

curve.  71 
volume,  69 

Pupil  reflex.  233,  267 

Purkinje-Sanson  images,  263 

Putrefaction  in  intestine.  135 

Pyramidal  tracts.  226-229.  235 

Reaction  time.  248 

Red  blood  corpuscles,  53,  90 

Reflex  action.  224,  229 

time.  232 
Rennin.  96 
Residual  air.  S3 

Respiration.  58.  60.  61.  318.  327 
innervation  of.  S3 

movements  of.  79 
of  muscles,  81 
rate  of,  83 
Respiratory  capacity,  82 

centre,  83,  238 

metabolism.  156 

quotient.  61,  159.  162,  187 

sounds.  83 
Reproduction,  6.  7.  307 
Retina.  269 
Rhodopsin.  271 
Ribs,  elevation  of.  79 
Rigor  mortis,  198 

Saddle-joint.  203 

Saliva,  92 

Salivary  digestion,  124 


INDEX 


Salivary  secretion,  93 

Salt-hunger,  166 

Salts,  excretion  of,  164 
functions  of,  115 
in  tissues,  15,  18.  172 

Sarcolactic  acid  (see  Lactic  Acid). 

Sarcoplasm,  189 

Scala  tympar.i,  289 
vestibuli,  288 

Schemer's  experiment,  263 

Sebaceous  secretion,  1 10 

Secondary  contraction,  195 

Secretions,  91 

Semicircular  canals.   241.    294 

Seminal  fluid,  307 

Sensations,  255 

Sense  organs.  255 

Sensory  areas  of  brain,  24s 

Serous  cavities.  88 

Serum,  52 

albumin,  56 
globulin.  56 

Sex.  differentiation  of,  323 

influence  on  metabolism.   176 

Silicon,   14 

Skatol,  51.  104,  136 

Skeleton.    l6 

Skin,   14,   16 
Sleep,  249 
Smell,  sense  of.  298 
Sodium.  13 

carbonate.   17 
chloride.   17.  97,   115,  164 
Sound.   292 

Space  sensation  of  retina,  276 
Specific  energy  of  nerves,  255 
Speech.  213 
Spermatozoa.  200,  308 
Sperrain,  308 
Spherical  aberration.  266 
Sphygmogram,  71 
Spices,   172 
Spinal  accessory  nerve.  252 

cord,  22C,  322 

nerves.  250 
Spiral  joint,  203 
Splanchnic.  102 
Spleen,  14.  16.  54.  55,  89 
Spontaneous  generation,  307 
Starch.  22 
Starvation,   164 
Steapsin.  98,   134 
Stereoscope,  283 
Stimuli.  3.   197,  2l8 

classification  of,  4.  195 
Stomach,  127,  132 
Strychnin,  232 
Successive  contrast.  273 


Sudoriferous  glands.  109 
Sulphur,  13,  43 

of  proteids,  27 
Supplemental  air,  82 
Suprarenal  glands.  78.  151 
Sweat  (see  Perspiration). 
Sympathetic  nerves,  75.  94.  253 
Synchondrosis.  201 
Synergetic  muscles.  206 
Synovia,  202 
Syntonin,  32 
Systole,  63,  65 

Tabes  dorsalis,  229 
Tactile  areas,  304 

corpuscles,  300 

sensations,  245,  300 
Talbot's  law,  273 
Taste  buds.  298 

sense  of,  298 
Taurin,  50 

Taurocholic  acid,  50,  100 
Tears,  no,  239,  283 

Teeth.  329 

Teichmann's  crystals,  34 
Temperature  of  body,  174,  180 

effect  of.  on  muscles,  189 
'  "  nerves,  218 
Testes.  154 
Tetanus,  191 
Thrombin,  56 

Thymus  gland,  89.  150,  151 
Thyroid  cartilage,  209 

gland,  150 
Thyroiodine,  151 
Tidal  air,  82 
Timbre  of  sound,  293 
Tissue  fluids.  87 
Transfusion  of  blood,  78 
Trigeminus,  251 
Trochlear  nerve.  251 
Trommer's  test,  19 
Trypsin,  08 
Tryptic  digestion,  133 
Tympanum,  286 
Tyrosin,  27 

Umbilical  cord.  327 
Urea,  43,  57,   104,   109 

compounds  of,  44 

formation  of.  45 
heat  value  of.   179 

Uric  acid,  35.  40,  57.  89,  104 
Urine,  103,  107 
Urobilin.  105 

Vagus,  74,  84,  86,  98,  99,  102,  133,  252 


INDEX 


339 


Yalves  of  heart,  66.  67 

of  veins.  74 
Vaso-motor  centres,  76,  238 

nerves.  75-77 
Vater-Pacini  corpuscles,  301 
Ventricles  of  heart,  66 
Vernix  caseosa,  321 
Villi.   103.  141 
Visual  angle,  277 

axis,  260,  277 

centre.  247 

field,  277 

perception,  276 

purple,  271 

sensations,  272 
Vital  capacity,  S3 

force,  I 
Vocal  cords,  210 
Voice,  209 
Voluntary  reactions,  225 


Vomiting,  128 
Vowels,  213 

Water,   14.  42.   160,   172 

functions  of,  15.  114 
lack  of,   166 
Wave  of  contraction,  190 
Weber's  law,  256,  272,  302 
White  blood  corpuscles,  54.  89.  199 
Wolffian  bodies,  320 
Work  of  muscles,   179,  180,  192 
unit  of,  178 

Xanthin,  104 

bases,  35,  47,  89 
Xanthoproteic  reaction,  3c 


Yellow  spot.  270 
Yolk  sac,  315.  3I( 


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